More validation of WDLs

[SHuang-Broad]

womtool validates based on syntax of the WDL, but the command block—a lot of times just bash—sometimes have errors and I'd guess few people run linters on the the command block with their IDE or text editor.

So, it makes sense for cromshell2.0 to validate at an ever deeper level, e.g.
https://stackoverflow.com/questions/171924/how-do-i-syntax-check-a-bash-script-without-running-it

I can take this on.

[lbergelson]

This is an amazing idea. Yes please!

[jonn-smith]

Ooh. This is a good idea.

Make sure to allow for the substitutions that cromwell makes (i.e. ~{varname} and ${varname} and potentially others depending on the command block itself). This will make the linting a little more complicated because the dollar sign dereferencing is also valid bash syntax, but the tilde symbol dereferencing is not.