[#651] regex compatability for headers matching

[geetptl]

Attempt at #651.

• Changes in header_matcher function.
• Instead of using simple list equality, it now checks for either regex or simple string check.
• Added tests test_request_matches_headers_regex, test_request_matches_headers_regex_strict_match

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (ad22f54) 100.00% compared to head (a2e2da1) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #663   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            9         9           
  Lines         2880      2968   +88     
=========================================
+ Hits          2880      2968   +88     

Files Changed	Coverage Δ
responses/matchers.py	100.00% <100.00%> (ø)
responses/tests/test_matchers.py	100.00% <100.00%> (ø)

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[markstory]

Thank you 🎉

[jgehrcke]

Nice, thank you!