Use PgUp/PgDn to turn pages of candidates

This is a common feature provided by many Bopomofo-IMs
as well as the Win32-chewing.

Codes are copied from chewing_handle_left/right.
Merge pull request #129 from hiunnhue/pgupdn_cand

Use PgUp/PgDn to turn pages of candidates
Move data files to usr/share/libchewing

Closed #121
Update test_del_bopomofo_as_mode_switch
Remove trailing whitespace
Merge chewing.pc.in and cmake/chewing.pc.in

Closed #132
Fix make release
Test make release in travis-ci