overhaul file writing system plus general updates

[bch0w]

Related to #75, #77 Internal rewriting of PySEP's file writing system to be more flexible and useful. Also minor typo fixes and bugfixes piggybacking

Major Changelog (default behavior changes)

• Changed default files that are written out by PySEP ("inv,event,stream,sac,config_file,station_list")
• No longer write out weights*.dat files by default, User must request using write_files='all' or write_files='weights_dist'
• Files are written out when available and not at the end of the workflow #77
• Log file (same as is printed to stdout) is written out as pysep.log #77

Minor Changelog:

• Turn off azimuth bins when sorting by absolute (back)azimuth #75
• Output stations file: stations_file.txt -> station_file.txt
• Allow User to bypass event_tag subdirectory #77
• Allow User to bypass SAC waveform subdirectory #77
• Added PySEP docs section to explain how to use subdirectory bypass
• Allow User to write out only specific components ('ZNE', 'RTZ', 'UVW') by passing parameter write_files=='sac_rtz' (for example) #77
• Allow Users to write out RAW SAC files (pre-quality control) with write_files=='sac_raw'