Use the platform-specific CA certificate locations if none provided
as per PEP-449 mirrors are deprecated
Add myself to contributors
Merge pull request #332 from ticosax/platform-ca-location

Platform ca location
CHANGES for #332
document and change HTTPHeaderDict, update CHANGES for bugfix
Merge pull request #333 from jschneier/master

document HTTPHeaderDict, update CHANGES for bugfix.
Formatting.