Read private repo credentials from a the netrc file

[Morriar]

Motivation

Add support for Tapioca to read credentials from a netrc file (defaulting to ~/.netrc).

Given these lines in your netrc:

machine raw.githubusercontent.com
  login $USERNAME
  password $TOKEN

Where $USERNAME is your Github username and $TOKEN is a personal access token. Then run Tapioca with the --netrc option (enabled by default).

The --netrc-file option can be specified to read another file than ~/.netrc:

$ bin/tapioca annotations --netrc-file /path/to/my/netrc/file

If the --netrc-file isn't specified, Tapioca will first try to find the netrc file from the environment by reading the TAPIOCA_NETRC_FILE variable then from ~/.netrc:

$ TAPIOCA_NETRC_FILE=/path/to/my/netrc/file bin/tapioca annotations

Closes #964.

Implementation

Tests