#100 Fixes readLen computation in unpackString
#100: Add a test case for pack/unpack large strings
#100: Add test cases of reading malformed UTF-8 strings
#100: Add test cases for FIXEXT. Fix unmappable UTF8 character check
#100: Add test cases to increase the code coverage from 83% to 95%
#100: Add a test for unmappable characters
#104: Fix assertion condition
Merge branch 'v07-unpacker' into v07-value
Merge branch 'v07-unpack-binary' into v07-value
Add visitor pattern interface. Rename some classes