Added explicit error message when --format is missing to AccessLog log parser
Added uWSGIParser. Can now be used with logparse --parser uWSGIParser.
Field names (for key-based -f lookup): 'ip', 'timestamp', 'method',
'path', 'bytes', 'processing_time'.
Added unit-test for the uWSGIParser
Better exception handling for the logparse utility, now reports failure to match
used-specified --fields in more accurate manner, separate from failures in actual parsing of the logline.