Make Request headers to be a dict of lists
Added migration for Request headers to be a dict of lists
Make code 2.6 compatible
pep8
Updated test to use new Request constructor
Updated _remove_headers to use latest Headers structure

Probably we need API in Request object like 'remove_header'
Fixed name of the variable
Updated _remove_query_parameters to use latest Request Api
Updated test for filters. Mock replaced with real Request object
Updated test to use new headers structure
Update _remove_headers to work with headers copy

Because of the filter implementation here we nedd to work only
with clone of the headers and request. subj to refactor
Removed accidental print call
Fixed typo
Merge branch 'feature/new-matchers' of github.com:mshytikov/vcrpy into feature/new-matchers