* Resolve java lint problem with soft link of directory.

* Ignore the soft link of directory.

* Add timestamp

* fix vid

* Address dutor's comment

* Address CPWstatic's comment and Add type cast handle in TraverseExecutor

* update

* update feroda deps

* implement delete a vertex

* address the comments of wadeliuyi and dangleptr

* address dangleptr's comments

* address comments of dangleptr and critical27

* address darionyaphet's comments

* Added support to singular forms for STEPS and VALUES

* Make VALUES unreserved

* enhance java client

* fix docs/nGQL-tutorial.md

Basic leader balance for storage, keep trying to trans leader from host with most leader to host with least leader, until all balanced.

Modify/Add two command in console:

1. "show host" will also display total leader count and leader count in each space
2. add command "balance leader", which will try to balance leader between different hosts

* test edge miss

* fix mutli version

* register gflags in meta client

* parse json

* try register at first operation

* address @laura-ding's comments

* fix ut, address comments

* address laura-dings's comments

* address comments

* address @dangleptr's comments, update gflags.json

* address @dangleptr's comments

* Ignore ccls configuration files

* Fix variable syntax document about load_data_interval_secs

* Cleanup unusable load_config_interval_secs configuration option

* Implemented type casting

* Address @laura-ding's comments

* Address comments

* Add build doc

* Address whitewum's comment

* Address yixinglu's comment

* Address whitewum's comment

* Modify SKIP_JAVA_CLIENT default is ON

* Add java jdk

* Modify spelling

* Modify resolve

* Add space size instructions

* add create-tag-edge, show and update get-started

* update

* update

* update

* update

* add FAQ

* update

* update

* update

* update

* file structure

* add create-tag-edge, show and update get-started

* update

* add FAQ

* update

* update

* update

* update

* file structure

* change build

* update

* update

* update

* update

* update

* last update

* update

* update

* update doc

* update

* update

* update

* update

* Issue#655 support for building with Clang

Compiled by clang 7.0.1((Fedora 7.0.1-6.fc29)

* Modified some of the code according to sherman's comments.

* add create-tag-edge, show and update get-started

* update

* update

* update

* update

* add FAQ

* update

* update

* update

* update

* file structure

* add create-tag-edge, show and update get-started

* update

* add FAQ

* update

* update

* update

* update

* file structure

* change build

* update

* update

* update

* update

* update

* last update

* update

* update

* add log

* update

* change graph

* change graph

* update log

* update log

* update log

* upload log

* update log

* update badge

* add create space syntax

* update link

* update

* improve unreserved keywords feature

support time to live

alter tag/edge drop column, and the column to be delete is as TTL column

address dangleptr's comment

* address laura-ding's comments

* rebase master

* Fixed crash problem due to meta not ready

* add comments

* Refactor clusterId and ActiveHostMan, change FLAGS_hosts_whitelist_enabled to be false by default

* Address all comments

This time only temporarily avoided this crash,
In issue #192, I will solve this problem for better.

* cluster depoly doc

* fix sherman-the-tank's comment

* fix graph port

* Enhance Java Importer

* fix ranking type

* update copyright 2019

* add README.md

*     Issue#424 to make `Expression::eval` to be able to do error handling.

    Summary:

    1. When the expression is evaluated, some wrong judgments are added,
       ifthe expression was failed, an error will be replyed to the user.

    2 fixed the crash when using mockStorageServer.

* 1 reformat the code.
2 Handled some errors.

* Implement union.

* Add distincter.

* Pipe have priority over set operator.

* Ajust error handling.

* Add distinct and implicit type casting for union.

* Inplement intersect and minus.

* Fix format.

* Adrress @monabobo's comment.

* Add result column names.

* Delete distincter and rebase.

* Rebase and fix conflict.

* Address @whitewum's comment.

* Address @laura-ding's comment and rebase.

* Fix crash problem when stop storage/meta daemon

* Address darion's comments

* Address wadeliuyi's comments

* Add fetch prop sentence.

* Add fetch executor.

* Refactoring expression.

* Accomplish fetch tag prop.

* Add ut for fetch vertex.

* Accomplish fetch edge.

* Add ut.

* Refactoring.

* Adjust ut.

* Fix format.wa

* Address @wadeliuyi's comment.

* Fix conflict.

* Refactoring.

* Add distinct support.

* Address comment.

* Fix conflict.

* Fix conflict and adjust distinct.

* Add default value for rank in EdgeRowItem. And collect prop after eval.

* Address laura-ding's comment.

* Fix link error after rebase.

It is used to ingest sst files directly after download files from hdfs.