fixes #550
Testing fsize option in reading sac files

Adds test cases for core.read() and SacIO.ReadSacFile()

See also #549
obspy-scan: plotting rectangles for gaps (instead of lines at start of gap) and new option --print-gaps
minor change to previous commit
fixes #553
fixing a bug introduced in 4e70c059e8f76d3e71da45d31ac31b6759f7b4b2

(IndexError in case of a gapless seed id)
fixes #554
Merge pull request #555 from obspy/554

fixes #554
removing a outdated comment
Making isSAC() more robust
signal: extend coincidence trigger

 - now has possibility to use event template waveforms
 - event triggers that excceed similarity levels get included in results
   even when network coincidence sum is not met
 - tutorial example
 - test, simple doctest for helper routine in cross_correlation
 - changelog
Added `lovrok` to required sac header fields
missing changelog entry for 4e70c059e8f76d3e71da45d31ac31b6759f7b4b2
Some modifications in isSAC()

- nvhdr >=1 (normally it is always 6).
  This avoids validating as sac files those files which
  have a lot of zeros at the beginning.
- lpspol, lovrok and lcalda are allowed to be undefined
  (though this is not good practice for a sac file...)
backwards compatibility for testing
Merge pull request #549 from claudiodsf/sac

Option to ignore file size check in reading sac files

works for me - thanks for fixing - merging ...
Merge pull request #545 from bonaime/waveform_enhancement

Waveform enhancement
More work related to responses
minor change for 0e58e40e4038952301bc20a4923022cb528d558b

- ignore channels that are not present in the stream to check
obspy-scan: correctly detect last gap in trace