Fix URI encoding

[johnf]

I was having issues with an oData (https://www.odata.org/) based API. oData uses queries like
http://example.com/todo?$skip=100&$top=50

Superagent will currently encode this to http://example.com/todo?%24skip=100&%24top=50

According to HTTP spec this isn't technically correct. While values of query parameters should have fill encoding applied, the list of reserved characters is smaller for the overall URL.

A correct implementation would be to use encodeURIComponent over the query values and then encodeURI over the entire URL. However, the approach I've taken is equivalent.

Some of the answers to https://stackoverflow.com/questions/4540753/should-i-use-encodeuri-or-encodeuricomponent-for-encoding-urls provide some more explanation. I can provide full detail from HTTP and HTML specs if required.

I tried adding a test but the serialize tests seem to be broken. I could only get them to run if I set NODETESTS=tests/client/serialize.js

[niftylettuce]

Thanks @johnf for your work here. I understand what you're saying - and it doesn't seem like your commit broke any tests judging from Travis. I would be curious if you could figure out the serialize tests, and what the issue is with them not working?

[johnf]

@niftylettuce if you check the Makefile it looks like all the tests inside clients are only run in the browser

[niftylettuce]

released to npm as v5.2.1