refextract: fix unassigned count_auth_group

• Initialised count_auth_group in main. (closes #487)

• Updated usage information with inspire journal title output option.

• When obtaining the recid and the file location for each extraction job, split a maximum of one time, since file names with arvix notation regularly include a colon e.g. 'arxiv:9834.pdf'.

• Display an error message, regardless of the output mode, and halt extraction when either a non-existent or an unreadable pdf/text input file is provided as input.