Allow page size to be set to 0

[wengxt]

Also, when page size is 0, change some behavior implicitly to allow simulate a
compose table like experience.

Fix #205

[iamchloya]

(My settings):

When page size is 1 (I move cursor by pressing left arrow. After pressing, the letter has written in text.):

When page size is 0 (i do same actions, but the letter was not writing. If i switch to another program, the letter disappears):

(attention to underlining).

[iamchloya]

i has used it with in /home/username/.local/share/fcitx5/
myinputmethod.tar.gz

If I need to enter a word that ends in a letter (which used in combination), then I need to press return/enter twice. I disabled the confirmation on return/enter, but I still need to press twice. (Example: most, post)

Also, "ctrl+c" is blocked in the terminal if I do not press enter/arrow left or right/ to "complete" the letter writting

Should I create a separate issue?

[wengxt]

@kuroya2mouse thank you for testing! Actually I did fixed that but I forgot to push it. Would you mind give it a try again?

[wengxt]

@kuroya2mouse Also, I suggest you to set PreeditCursorPositionAtBeginning to false. That should make it feel more natural.

[iamchloya]

IT'S REALLY WORKS. THANKS THANKS THANKS THANKS THANKS

If i notice any bugs, i'll let you know