feat: add support for x-forwarded-host

[dinoboff]

Adds trustProxy option to HMAC_SHA1 and Provider constructor.

It overloads the Provider constructor with the third argument being either a nonceStore or an options object (for a nonceStore, a signer and the trustProxy flag):

new Provider(key: string, secret: string, options: NonceStore|{nonceStore: NonceStore, trustProxy: boolean, signer: Algo}, signer: Algo)

[coveralls]

Changes Unknown when pulling 4e31b364129f7a50fa6f811e0b2e8d985b0c3a63 on dinoboff:fix/67 into ** on omsmith:master**.

[coveralls]

Changes Unknown when pulling 420de9d60c15183d48b84b63af6f58894c7e9d8f on dinoboff:fix/67 into ** on omsmith:master**.

[coveralls]

Changes Unknown when pulling 420de9d60c15183d48b84b63af6f58894c7e9d8f on dinoboff:fix/67 into ** on omsmith:master**.

[coveralls]

Changes Unknown when pulling a2b1ed5c4554a8ab3f9021c59445f75c7a3b56c3 on dinoboff:fix/67 into ** on omsmith:master**.

[dinoboff]

Ready for review.

Note that it's my first PR using coffee script; please point to missing coffeeish idioms.

[dinoboff]

I published it as a scoped package: https://www.npmjs.com/package/@dinoboff/ims-lti (I don't think npm can install the fork directly from github).

[coveralls]

Changes Unknown when pulling 72c513a839fe87aac06307d1c096ea14951245e0 on dinoboff:fix/67 into ** on omsmith:master**.

[isaacagudo]

@dinoboff, thanks for your contribution. I tried to solve the issue checking the header before noticing your pull request. I think we need a more stable node library (I have nothing against Coffee, only that I haven't used it before).