remove dead code

the parameter to testmod() must be a module, there's no SessionCache
module, morover, there are no code examples in module for doctest to
verify
simple unit tests for ClientHello class (v3)

Implement unit tests for the Client Hello class and its methods,
includes tests for sending certificate types extension, srp username,
tack, npn and server name. Minimal test for parser.

v3:
run using test case discovery

v2:
fixed syntax error in test_write()
ServerHello unit tests

add unit tests for ServerHello class methods
test NPN extension sending
add minimal tests for parser with bad input
Merge pull request #29 from tomato42/test-suite-2

trivial cleanup, start of unit test suite (from Hubert Kario)