Dont escape exclamation (!)

[mniak]

I dont understand why the exclamation is escaped in this library.

I intend to make a pull request making the escaping of ! an option that could be disabled.

If you agree, we could turn this off by default.

[mniak]

Implemented in #173

[joho]

My intention for this library is to maintain generic compatibility with the other dotenv libraries.

If the library's behaviour here is inconsistent with the ruby or node implementations, then I will accept a change to make it consistent. If not, I will not add a flag to enable an incompatibility mode.

Thanks.