Merge pull request joho#58 from lucastetreault/master

feat(Expand Variables): Custom variable expansion instead of Go's os.Expand

Version 1.2.0

Added in this version:
- Added Marshal, Unmarshal, and Write methods to write .env files back to disk (or string) joho#35 joho#41 joho#42 thanks @alexquick
- Added Parse(r io.Reader) to read env out of streams joho#36 thanks @pda
- Small parsing fixes joho#34 thanks @alexquick
- Some repository quality of life stuff joho#33 thanks @crash7