Cleanup dialyzer plt building in Makefile

Use ~/.dialyzer_plt along with a custom dependencies only plt.
Dialyzer warning fixes
Canonicalize all response headers in main s3_request helper function

This fixes a bug where we failed to fill out the object meta data
because we were expecting normalized header names.
Include headers in non 2xx responses that are thrown as error

This could be a compat breaking change depending on how calling code
is matching on the error response.
Merge pull request #8 from opscode/canonical-headers

Canonicalize response headers, fixing get_object_metadata
Removing app vsn regex
Updating dep to use Opscode fork of ibrowse
Merge remote-tracking branch 'opscode/master'

Conflicts:
	src/mini_s3.erl