Adjust index structure and tools.

Changes:
1. Integrate sort and maketree into init_database.
2. Let freq live in index tree leaves, out of dictionary.
Let dict & tree buffers be const.
Remove redundant pho_id in PhraseIntervalType.
Rename variables for parent of phrases.
Integrate char functions into dict.

char.c and char-private.h are removed.
Integrate name of Get*First() & Get*Next().

"vocabulary" contains both "phrase" and "word".
Compress TreeType to 8 bytes.
Separate `dict' & `tree' access.

dict.c / tree.c only accesses dict / tree.
Data exchange is through tree_cur_pos & tree_end_pos.