rl_helper: add history command management

We need a growable buffer which will store a list of command strings. So
when we press up or down keys, our line buffer is replaced with old
commands that we typed.

This also fix a possible bug, cause we pass a copy of line buffer to
line processing callback. So we don't will have problems if we change
it's value (eg strtok).
Add a generic Write Characteristic command

This method will be used as helper to each specific write characteristic
command.
Add Write Request Characteristic command
Add Write Command for characteristic
Add write characteristic callback