mseed_ext: corrected type of psamples argument
docs: added an example snuffling to demonstrate how markers are created
snufflings: added support for directory snufflings

The $HOME/.snufflings/ directory may now also contain directories
containing a special-named file 'snuffling.py'. If such a file exists,
it is queried for snufflings as usual.

The snuffling can access its own directory name in its '_path'
attribute.
moment_tensor: added possibility to generate random MTs
Merge branch 'master' into fomosto