Refactoring: move members from WEdit to edit_buffer_t and rename related functions:

WEdit::last_byte -> edit_buffer_t::size
WEdit::total_lines -> edit_buffer_t::lines
WEdit::curs_line -> edit_buffer_t::curs_line

edit_count_lines() -> edit_buffer_count_lines()

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
Refactoring: rename functions of getting BOL and EOFL:

edit_bol() -> edit_buffer_get_bol()
edit_eol() -> edit_buffer_get_eol()

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>