Add FILE_LICENCE declarations to almost all files that make up the
various standard builds of gPXE.

Intel's C compiler (icc) chokes on the zero-length arrays that we
currently use as part of the mechanism for accessing linker table
entries.  Abstract away the zero-length arrays, to make a port to icc
easier.

Introduce macros such as for_each_table_entry() to simplify the common
case of iterating over all entries in a linker table.

Represent table names as #defined string constants rather than
unquoted literals; this avoids visual confusion between table names
and C variable or type names, and also allows us to force a
compilation error in the event of incorrect table names.

permanent processes, rather than requiring each one to have its own
initialisation function.

Add reference-counting to processes.

Add timer_running() test.

Yes, you really can do it in 65 bytes.