Correctly handle 0 in str-slice.

Closes #1330
Include the filename in newline deprecation warnings.

Closes #1319
Properly convert selectors with newlines to SassScript.

Closes #1320
Properly handle newlines in string interpolation and +.

Closes #1331
Avoid errors in Color#with.

Closes #1333
Merge branch 'stable'

Conflicts:
	doc-src/SASS_CHANGELOG.md