#39: add authinfo/netrc parsing and .gpg support

[tzz]

The discussion for #39 applies. Git credentials are not implemented, but authinfo and netrc files, with and without .gpg extention, are checked. Please review, especially the hack to pass a pipe to load_file (maybe we need a warning if gpg is not in the PATH?).

[timkay]

Wouldn't it be better to simply do this:

$secrets_file ||= "gpg --decrypt $home/.$_.gpg|" if -e "$home/.$_.gpg";

and skip the whole clause below?

[tzz]

Then you couldn't do --secrets-file=/home/tzz/.awssecret.gpg. I wanted to be able to decode any credentials file, authinfo/netrc or "classic" style.

[timkay]

ahh. good point... I'll merge your code.

[tzz]

Thanks!