Parsing fixes for ORCA xTB (Fixes #44)

[TroyNSmith]

Updated parsers.ORCA.parse_natoms to be optional (for cases like xTB where regex patterns are not maintained).

[coltonbh]

@TroyNSmith - Will look at this today! Sorry to keep you guys waiting. GitHub didn't send me a notification for this :/ Be sure to @coltonbh when something is ready so I get notified :)

[coltonbh]

@avcopan and @TroyNSmith released in qccodec v0.10.2. Please @coltonbh me when something is ready to go--sorry I left you hanging on this one! Didn't know it was ready for review and GH didn't notify me.

[avcopan]

Sorry! I assumed GH would ping you either way. Thanks, @coltonbh !

[coltonbh]

Usually does! Didn't for some reason.

Also, I'm done with my dissertation defense! So it's time to get serious about these software stacks! I'll still be finishing the written portion of my dissertation this summer, but I want to provide same-day or at least 48-hour turnaround on any of your issues here, @avcopan and @TroyNSmith. This fall, I'll be full time and do a major overhaul. Let's go!! 🚀