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>
FIXFOR: Start of edit buffers refactoring.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
Refactoring of functions that operate with editor buffer.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
Add functions to transform string to unsigned integer:

 * (xstrtoumax): from gnulib.
 * (parse_integer): from coreutils (dd.c).

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
FIXFOR: Use GPtrArray to store editor buffers.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
Drop limit of edited file size.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
Add thershold for fiel size.

Add "editor_filesize_threshold" ini option to ask whether open file
if it size is larger than specified thershold. Supported string value
formats are: "640000000", "64000K", "64M". Default value is 64M.

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