PPSD: enable getting/plotting mode and mean psd values
Replacing GPL spline code by LGPL spline code

Now using the LGPL SPLINE library
http://people.sc.fsu.edu/~jburkardt/c_src/spline/spline.html

Adding an extra test, as the current obspy tests do not seem
to cover the interpolation part.

See #827.
pep8
typos and py3k
Trigger length of 1 sample (on==off) resulted in empty array.
Replaced if else with try Except to avoid unnecessary if checks.
x axis inputs must be strictly increasing

thx to @QuLogic for pointing that out
Merge branch 'master' into ppsd_stats
minor refactoring
std of single value is always 0
beautifying
Add ZMAP write support for earthquake catalogs
Improve python 3 compatibility

...by explicitly encoding/decoding strings when writing/reading to files.
Fix minor issues
Open files in context, minor improvements
Minor improvements
Add ZMAP read support
Remove unused doctests
Move ZMAP support do dedicated package
Fix python 2.6 compatibility