bump to 0.4.1

update CHANGELOG and bump to v0.4.0

this closes mrtazz#38

update CHANGELOG for 0.3.0 and bump version

v0.2.0 (19th April 2015)

- support basic auth
- Add header's to response object
- fix memory leaks related to curl cleanup
- add autotools build
- add CONTRIBUTING.md
- add vendorized gtest

- don't call exit(1) but return -1

- improve include structure
- some documentation fixes

improve build system and header inclusion

- meta.h is included locally
- add static library build
- add dynamic library build

following HTTP methods are supported:

- get(url)
- post(url, contenttype, data)
- put(url, contenttype, data)
- del(url)