Change key mapings for insert mode

[tehnodev]

My suggestion for insert mode shortcuts is to use them similar to normal mode movements for easier remembering.

Delete previous char ctrl-h (it is current mapping) ok, same as 'esc h c'
Delete next char ctrl-l (lowercase L, instead of ctrl-d) same as 'esc l c'

Delete previous word ctrl-b (instead of ctrl-w) same as 'esc b c'
Delete next word ctrl-w (instead of alt-d) same as 'esc w c'

Delete to start of line. Using normal mode would be 'esc vgs c', but ctrl-s is already mapped to Commit undo checkpoint. So i suggest to use ctrl-i, similar to 'esc I' (uppercase i, which inserts on beginning of the line)

Delete to end of line. To be consistent with deletetion to line start, i suggest to use ctrl-a (instead of ctrl-k) similar to 'esc A'.