Textfields char count (and bugfixes)
Adds a character counter to SingleLineTextfield. I think this is quite close to the spec, but I still need someone else's opinion
Can be used by adding:
max_text_length: [number]
Also fixes the bugs related to textfields in #41
Causes of bugs:
Red hint text: Was caused but theme_text_color
being set to error, which was leftover from old revisions
Hint text duplicates: Kivy was adding the hint_text on focus, and even though the color was [0,0,0,0]
it still displayed. Fixed by overriding the function that refreshes the hint text