AddKeyValue for TextDict
Fix bug of UTF8Util::FromSubstr
Fix string truncation
Unit test for TextDict

Add a constructor for DictEntry with key and single value
Fix build warning of -Wreorder
Add CMake scripts for libopencc and TextDictTest
Fix bugs of DartsDict and add unit test
Implement DictTestUtils to handle TextDict creation and test
Fix a bug of TextDict::GetLexicon

This function is guaranteed to return sorted lexicon
Test all lengths of match of dict
Rename GetLengthsOfAllMatches to MatchAllPrefixes
Use shared_ptr at TextDict::GetLexicon
Use shared_ptr at MatchAllPrefixes, etc to reduce copies
Use more shared_ptr and reduce members for serialization of DartsDict
Make GetLexicon a member of abstract class Dict and add LoadFromDict to TextDict
Implement serialization for TextDict
Serialization and deserialization for DartsText based on TextDict

Values can not contain space for now :(
Should be fixed later
Add unit test for DictGroup