v2.3 - Bug fixes, operator precedence, parsing comments in-place

• Fixed some bugs I accidentally left in the previous release regarding the output directory and extension variables from argparse
• Brought in better operator precedence from logidiff
• Double-checked the LRM and thus removed nand and nor operators
• Implemented parsing comments in-place with the --parse-comments flag, that treats commented directives as though they aren't commented, and overwrites the original file:

  vhdlproc *.vhdl --parse-comments # parse commented directives and overwrite original file
  ghdl -a --std=08 *.vhdl       # same exact files that were passed to vhdlproc
  ghdl -r --std=08 testbench    # run simulation