pinyin_parser: updated so file install dir.

the old design have flaws and limitations. see :id001: and :id002: in
operational file.

new design:

open :memory: db readwrite, this will be the m_db handler.

try attach main db at known path (readonly if possible) to "maindb".
if failed, try next known path,
if all failed, initDB() should return false and gave up.

try attach user db at known path to "userdb" schema, if failed,
create :memory: db and initialize it as user db. attach it as "userdb"
schema.

update all query against main db to query from maindb.* table.
update all SQL against user db to run again userdb.* table.

benefits:
- access to user db is concurrent safe. multiple libpyzy app won't overwrite
  user's user db file and lose data.
- there is no need to saveUserDB() using timer in the bg.
- there is no need to copy data from user db to :memory:, if user db is
  large, this can lower memory usage.

- add error handling for all db operations
- refactoring Database.cc to make it more readable.
  add doc for Database.cc
  extract method copyDB(), initUserDB(), setPragmaOnMainDB()
- fix old timeoutCallback(), now named cb_saveUserDB()
  saveUserDB() should not be in the condition, because save can fail endlessly
  if file system have problem.
- no longer require main db to be a regular file. symlink should work fine.
- drop the dreaded overly reused class variable m_buffer. use meaningful names
  in current context.
- escape string in SQL statements
- update meson.build
  add prefix in PKGDATADIR
  define glib logging domain
  disable glib asserts for release build
- I will use so file version in git log.

BUG=https://code.google.com/p/pyzy/issues/detail?id=1
TEST=None

Review URL: https://codereview.appspot.com/6943055

BUG=None
TEST=Manual

Review URL: https://codereview.appspot.com/6307059

BUG=Database::query crashes on some situation
TEST=Manual

Review URL: https://codereview.appspot.com/6295043

BUG=None
TEST=Manually

Review URL: https://codereview.appspot.com/6201053

BUG=None
TEST=Builds manually.

Review URL: https://codereview.appspot.com/5903060

replacing
- gchar - char
- gint - int, unsigned int, or size_t
- guint -> unsigned int or size_t
- guint8 -> unsigned char
- gboolean -> bool
- gsize -> size_t
- gpointer -> void *
- gconstpointer -> const void *
- gunichar -> unichar (typedef of int on PyZyUtil.h)

BUG=None
TEST=Run a test

Review URL: http://codereview.appspot.com/5367046

- Add many APIs to replace processKeyEvent.
- Remove pager related codes.

BUG=None
TEST=Run a test

Review URL: http://codereview.appspot.com/5314054

This CL don't modify files under debian/*.
Some files which is removed by http://codereview.appspot.com/5305041/ are also unmodified.

BUG=None
TEST=Manually

Review URL: http://codereview.appspot.com/5301043

BUG=
TEST=

Review URL: http://codereview.appspot.com/5235062