can't detect requirements.txt from subfolder

[oscarlevin]

I think that if you try to run a pretext command from a subfolder, then requirements.txt is not being read. Of course, we allow you to run pretext from a subfolder, so we should look for requirements.txt from the root of the project.

[oscarlevin]

Okay, I no longer think it is the subfolder, but that I specified pretext >= 2.6.1 is requirements.txt. But this should also be supported.

[StevenClontz]

While CLI sticks more or less to semantic versioning, core PreTeXt does not. So it's quite possible a build with 2.6.1 looks quite different than a build for 2.6.3. I'm concerned that being loose with versions here will cause headaches down the road.