Update CMakeLists.txt and NEWS to release OCE 0.15

Bump OCE_ABI_SOVERSION, this version is not binary compatible
with OCE 0.14.1.
Fix whitespace to follow Markdown syntax
Remove mentions of FTGL, it is not needed since OCE 0.13
Mention license in README.md
Added travis-ci and googledrive urls
Merge pull request #476 from tpaviot/review/release-OCE-0.15

Update CMakeLists.txt and NEWS to release OCE 0.15