Change zuinBuf to bopomofoBuf
Add test cases for aux buffer
Use char[] to store aux buffer
Remove wch_t

Closed #23
Fix indent
Add AUX_PREFIX_LEN for aux buffer prefix
Store aux buffer only in ChewingData
Implement chewing_commit_preedit_buf
Add document for bopomofo, preedit, commit buffer
Fix warning: call to __builtin___strncat_chk
Implement chewing_clean_preedit_buf
Add error handling test cases for new APIs
ADd test-logger.c back for NULL logger test
Avoid using strncat

It is too easy to use strncat wrong.
Check return of asprintf to cease warnings
Cease warning
Cease warnings