TINKERPOP-937 Extracted "provider docs" to their own book.

[spmallette]

https://issues.apache.org/jira/browse/TINKERPOP-937

Moved from the standard reference documentation. Added links between the docs where necessary. Published docs for review here:

http://tinkerpop.apache.org/docs/3.1.2-SNAPSHOT/dev/provider/

VOTE +1

[spmallette]

@velo watching the appveyor build. looks like we got a clean one on the branch but a failed one on the pr...maybe just a fluke with hadoop? thought you might want to look at the logs....

if anyone is reviewing this, i wouldn't worry about the single appveyor failure - the other three builds were good.

[velo]

Should be a race/timing issue...

Failed tests: 
  GroovyProfileTest$Traversals>ProfileTest.g_V_sideEffectXThread_sleepX10XX_sideEffectXThread_sleepX5XX_profile:173 Duration should be at least the length of the sleep (59ms): 53 

Tests run: 1722, Failures: 1, Errors: 0, Skipped: 821

[pluradj]

VOTE +1

[okram]

VOTE +1.