Add -nodefaultscript option to allow overriding builtin.fbfrog
Rename builtin.fbfrog => default.fbfrog
Rename builtin.h => default.h
Fix & update .gitignore, only ignore files in root dir as intended
Add include dir searching for @files

Now @files (including default.fbfrog) and other resources such as default.h
will be searched in
	<curdir>
	<exepath>/include/fbfrog/
	<exepath>/../include/fbfrog/

* include/fbfrog/ becomes a "library" of common *.fbfrog or *.h files
  which are useful for many fbfrog use cases
* but local files in <curdir> still override those from include/fbfrog/
* This allows fbfrog to be installed into /usr or /usr/local etc.
* but at the same time it can still be used as "standalone" program,
  extracted in the home directory or similar, which is useful for
  development too.
Clarify rename lists
Fix merging of number literals which have same digits but different base

(b91d2c8dc4e875de15c2fd429eca520effada4fd regression)
tests: Demo broken callconv merging behaviour
Fix merging of procdecls with same callconv but different EXTERN blocks
astMergeVerblocks(): Clarify commentary