Generate Header Guard: Sanitize File Name

[hattesen]

When generating the header guard macro, the contents of the pattern string (including the resolved {FILE} variable) should be sanitized by replacing all non-alphanumeric characters by an underscore character (_).

Currently, a header file my-header.h' causes a header guard macro like: MY-HEADER_H, but it should be MY_HEADER_H`, ensuring a valid macro identifier.

Similarly, it would be nice to have a variable holding the header file name extension (e.g. {EXT}), allowing header guard macros to match the header file extension (.h, .hh, hpp, 'hxx), rather than the current hardcoded (_H`) to ensure unique header guards where multiple header files exist which differ only by file name extension.

I would be happy to submit a pull request for this feature-change.