Replace setup_method() with auto-use fixtures
Enable signals in main() instead of Interpreter.__init__()

Tests must now explicitly setup signal interception if they need it.
This allows Ctrl-C to work as expected while running most tests.
Correctly reset signal handling in tests
Updated reasons of failing tests
Implemented crc32
Removed extra changes from conftest and removed commented line
Removed the comment from the failing test
Implemented hex2bin
Reimplemented crc32 based on PHP implementation
Added implementation note
Implemented levenshtein
Implemented quoted_printable_decode and quoted_printable_encode
Implemented str_shuffle
Fixed call to min to be compliant with Rpython
Fixed the way the hex digits are generated
Fixed str_repeat test
Fixed strstr test
Fixed failing message for strlen
Fixed failing message for strjoin_error
Fixed strpos