Fix generate-cmakefiles to make callable and allow root directory to be ste

[Prof Garth Wells]

The script ./cmake/scripts/generate-cmakefiles must at present be called from the top-levrl directory. It would be tidier if it could be

1. Called from another Python script; and
2. The root directory could be set.

When this is fixed, the file doc/source/conf.py should be simplified when calling generate-cmakefiles.

We need to call this script on read-the-docs from conf.py to make the CMake files accessible.

[Anders Logg (Chalmers)]

Is it enough to make the script be callable from anywhere? (And that it figures out the root directory itself.)

[Prof Garth Wells]

Yes, but neater if the root can specified if desired.

[Anders Logg (Chalmers)]

Removing milestone: 1.8 (automated comment)