Major change in isisscripts build process (new makestatic)

This commit represents a major change in the isisscripts build process.
The old makestatic script has been replaced by a new script that will
hopefully yield a much more stable build process for the final
isisscripts.sl.

Important changes are that it is now not necessary anymore to insert
any checks that external modules have been loaded successfully. This
is done in a consistent way by makestatic. In addition, the new build
process does not require authors to do a "require" for any functions
that are internal to the isisscripts. These requires have been removed
from all isisscripts routines with the exception of Mike Nowak's
scripts.

Functions that were missing from older isis versions such as
wherefirstmax, sincos, and so on, are now consistently defined and
have been removed from other sl files (they are now locaed in
src/slang/compatibility). You can therefore always assume that they
exist.

The README has been updated.