Autocommands for automatic layout updates

Hi,

Tried to improve layout management.

Solved issues (see #37):
* `:new`
* `:help`
* `:q` and similar

Remains:
* `:split` without arguments from master
* `:Ex` netrw has lots of deep magic so I disabled event handling for buffers with `netrw` type

Please, check carefully before merge =)