Dealing with strange seg2 files.

It now strips all non printable characters. This should work in
all cases.
Merge remote-tracking branch 'krischer/seg2_fix' into releases
clean up after lion :P
Fix links to Mini-SEED information.
Fix links to XML-SEED documentation.

The page numbers also appear to need an update. I think these are the
correct ones.
Fix SEED links in documentation.
Merge pull request #746 from QuLogic/seed-weblinks

Fix SEED weblinks
update credits

thanks for reporting problems and helping with fixes @QuLogic!
Merge remote-tracking branch 'upstream/releases'

Conflicts:
	obspy/seg2/seg2.py

not sure if I put the decode at the right place in seg2.py while merging
for python3.. (@mbyt, @krischer)
update credits sorting order
temprorary fix for tutorial doing seismometer correction based on old
IRIS web services. Whole section needs refactoring.. :(
Python 2 and 3 compatibility for 90bcc3a44ec1430b4.
add Bode plot to Response object
changelog
Response plot: add line cross for instrument sensitivity
response plot: changes to call parameters

- more intuitive for users to be able to specify sampling rate +
  frequency step (i.e. min/max/step of frequencies) in plot (rather than
  t_samp and nfft)
- make it able to provide two axes for the plotting instead of making a
  new figure (will be used in plotting multiple channels in
  Station/Network/Inventory)
response plot for Channel class
Response/Channel plot: make it possible to pass in label string for
legend
Station plot: response plot working but might need some more work..
Station.plot(): only leave option to plot response

makes it simpler and clearer, for a map location plot it is probably
easier to nest the station into a network and use that for plotting