Add srf module

[lispandfound]

What is this module?

This module allows for both reading and writing SRF files.

Why not use the module in QCore?

For a few reasons:

1. The qcore.srf module does not support writing SRF files.
2. Exposing SRF points as a pandas dataframe allows manipulation of the points using efficient vectorised operations. We use this in rupture propagation to delay ruptures by adding to the tinit column.
3. There is better documentation for the new module than the old one.

Example

>>> srf_file = srf.read_srf('/path/to/srf')
>>> srf_file.points['tinit'].max() # get the last time any point in the SRF ruptures
>>> srf_file.points['tinit'] += 1 # delay all points by one second
>>> coordinates.wgs_depth_to_nztm(srf_file.header[['elat', 'elon']].to_numpy())
#   ^ get the coordinates all the fault plane centres in the rupture in NZTM format
# etc...
>>> srf.write_srf('/path/to/srf', srf_file)

[AndrewRidden-Harper]

nice description of the differences with qcore.srf