Add man page

Mantaining an unstructured documentation file, such as README, is cumbersome.
Also, a man page greatly improves the documentation quality
pkg_archlinux: install man page
update README
luatodo: add config file generator routine

The config file generator routine makes luatodo self contained. From now on,
getting started with luatodo is as easy as typing "luatodo -g".

The generator routine accepts a config file name from the command line; in case
it is not provided, defaults do "./.luatodo". Also, a dash represents stdout.

Internally, I had to write a little helper function, getVal, that "stringifies"
lua values. It works for numbers, booleans, strings and tables. About the
latter, indices must be integers but supporting other types of indices won't be
hard (as long as getVal supports the index type).
Merge branch 'devel-doc' into 'master'

* devel-doc:
    update README
    pkg_archlinux: install man page
    Add man page