Issue warning using python warning in 'sigproc.py'

Use python's warnings.warn instead of simply printing a string to stdout.
Add a python module for reading filterbank file.
Add script for injecting psr into filterbank data
Try to reduce memory usage of 'injectpsr.py'
Modify 'filterbank.py' to use memmap numpy arrays
Fix bug where code crashes if no remainder.
Added function to create polycos from parfile.

Also, added some functions to get rotations, frequency, phase at given MJD.
Merge branch 'polycos' into inject
Merge branch 'inject' of github.com:plazar/presto into inject
Re-factor how 'injectpsr.py' deals with pulse profiles.
Move 'injectpsr.py' to bin dir and add execute permissions.
Add missing '!' in hash-bang (#!) in 'injectpsr.py'
Re-factor 'injectpsr.py' to make it easier to run the profiler.

The code is slow.
Major changes to 'injectpsr.py' to get it working.

Still needs more testing.
Add soft link to 'injectpsr.py' in lib/python dir so it can be imported more easily.
Fixed bugs in create_filterbank_file() in filterbank.py that were assuming function was part of a class that no longer exists.
Add pointer to 'bin/injectpsr.py' into 'lib/python' so it can be imported if necessary.
Add ability to append spectra to filterbank format files via python FilterbankFile objects.
Check if FilterbankFile is writable.
When injecting append spectra to empty filterbank file instead of copying and modifying.