Update release number for 0.5 release (graphframes#199)

* updated release numbers to 0.5.0

* Update travis branch to track latest Spark 2.1 release version (graphframes#198)

* Update travis branch to track latest Spark 2.1 release version
* update Makefile and build.sbt default

[157] Updates for 0.4.0 release (graphframes#179)

Minor doc updates

prepare release v0.3.0 (graphframes#138)

Prepare release 0.3:

update README, versions
update API doc in CC
hide protected methods in Logging

* prepare release v0.3.0
* do not mention python 3

Merge pull request graphframes#103 from thunterdb/95-update

[95] Official release numbers

Merge pull request graphframes#35 from thunterdb/1602-error

typo in test