Parser improvements.

For files with multiple versions in the format TXC_2-AIRP-x-sj2.xml, the script will choose the current file as per https://tdx.131500.com.au/download/files/TransXchange_Data_Release_Notes_V_2_2_121018.pdf

Don't write unneeded files
Write needed data to one file (<filename>-data.json)
Add support for choosing files based on date
Automatically "fix" the json. The json is now written so that the variables are assigned accurately.
Added dependency on 'cat' and 'grep'. Sorry, Windows.