Add lang/toString
Typecast values to string in string/* methods, and general cleanup
exit with proper status code when some spec fails. closes #25
add string/WHITE_SPACES spec. closes #26
remove check-coverage command from travis since it isn't really important and it's probably causing issues. see #25
Update changelog
Merge pull request #24 from conradz/string-cast

Convert values to string in string/* methods
Add `lang/toString` to changelog