Bug Tracker ref & SemVer

Red color removed in Wiki, as a red link in a wiki says there is no page behind.
Update README.md
Merge branch 'master' of https://github.com/ozh/YOURLS
Merge branch 'master' of https://github.com/YOURLS/YOURLS
Merge branch 'master' of https://github.com/YOURLS/YOURLS
Better error reporting on install. Fixes issue #1347.

Also, remove unused function.
Merge pull request #1367 from ozh/check-db-ver

Better check on DB version