improve command line utility

[mcroomp]

• Use a real, but tiny argument parser (unfortunately this means all the switches now get -- as per unix standard)
• Add option to scan a whole directory and verify that the compressor works
• Include the option to run cpp version of lepton to verify that the files are all decompressable by the standard version

[Melirius]

LGTM, what do you think about lifting the Lepton file size limit here also? Or introducing command-line switch for it?

[Melirius]

And there is an error in WASM version about thread priority, it needs guards then. As well as on Linux.

[mcroomp]

LGTM, what do you think about lifting the Lepton file size limit here also? Or introducing command-line switch for it?

Added the filesize limit to enabled features so it can be overridden