Add a shout-out to Alexander Pavlov for sourcemaps.
Fix minimum-specificity calculation when trimming @extend output.

Closes #511.
Merge branch 'stable'
Update SASS_CHANGELOG.md: missing space

A little typo.
Merge remote-tracking branch 'origin/stable' into stable

Conflicts:
	doc-src/SASS_CHANGELOG.md
Merge branch 'stable'

Conflicts:
	VERSION
	doc-src/SASS_CHANGELOG.md
Merge remote-tracking branch 'origin/master'

Conflicts:
	doc-src/SASS_CHANGELOG.md