Few fixes and the new function to crop components

[vladimir-popov]

The new function crop

require('lualine.ex').crop({str}, {cmp})

Crops the component when its length longer than {max_length} option (if it's specified).

Parameters:

* {str}           (string) the current value of the component.
* {cmp}           (table) the component object with follow options:
    * max_length  (number) the maximum count of symbols in the component, 
                  after which the component will be cropped. If it's absent
                  or less or equal zero, the function returns nil. Default
                  to nil.
    * crop        (table) crop options:
        * stub    (string) a string which will be used instead of cropped
                  part. Default to '…'.
        * side    ('left' | 'right') a side from which a value will be
                  cropped. If absent, it will be calculated from the
                  component's section: for sections a,b,c a component value
                  will be cropped from the left; for sections x,y,z from the
                  right.

Return:

Original or cropped string.

This function is applied to the ex.git.branch component as the fmt function by default.

Fix of the ex.component

Reference to the component is passed to the fmt function.

Fix ex.git.branch component !

Fixed typo in {committed} option. This is breaking change!

Fix ex.cwd component

The count of symbols is used to follow the max_length options instead of the count of bytes.