Add Marshal, Write, and Parse(reader)

Added in this version:

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