package: update "superagent-proxy" to v0.1.0

Includes `http.Agent` caching among some other goodies...
bump superagent to 0.15.7
History: remove trailing whitespace
Package: minor lint fixes
Package: re-implement the .netrc auth logic

Support for the .netrc auth was removed in 6a04a0c9623a325a9d81450daf06e44044ce4f65.

Now the auth encoding logic is normalized into an external function,
which both the .getFile() and .getJSON() functions use.

As an added bonus, manually passed in auth credentials now work with .getJSON().
Previously only the .netrc file would be accounted for.
component-install: fix the --proxy option

Otherwise it's a Boolean, not a String...
Really? What is this?!?!
Merge pull request #440 from component/fix/netrc

Package: re-implement the .netrc auth logic
Package: re-implement proxy support

Since we're not using superagent to get the package files,
superagent-proxy wasn't really taking effect. I've extracted the
proxy agent mapping and caching logic into the `proxy-agent` module,
so that we can use it directly with the `http`/`https` modules.

This fixes the --proxy and/or `http_proxy` env variables for realz
removing proxyAgent (since we're using superagent anyways)