perf(Request): Use a list comprehension and don't lowercase the headers

List comprehensions are faster than generators. Also, there is no
need to lowercase the header name, since headers are case-insensitive
after all.
fix: Add output encoding to tests for Python3

In certain environment setups python 3 will detect the appropriate
output as ASCII and will fail when trying to write a unicode string.
Override this by forcing UTF-8.
Merge pull request #201 from jaypipes/utf8setup

Ensure long description is Unicode string in setup
Merge pull request #188 from jamielennox/py3-tests

fix: Add output encoding to tests for Python3
Merge pull request #193 from kgriffs/master

perf(Request): Use a list comprehension and don't lowercase the headers
Merge https://github.com/racker/falcon