#86 add support for %(ADD|DEL)(HEAD|TAIL)(I)

[nasm64developer]

In certain scenarios it would be handy to be able
to modify an existing multi-line macro definition.
That is, sometimes the ability to add a new line
to the beginning or end, or remove the line at the
beginning or end, would be handy.

Attached you can find preprocessor changes, which
introduce the following new directives:

%ADDHEAD(I) mmac_name param_count new_line
%ADDTAIL(I) mmac_name param_count new_line
%DELHEAD(I) mmac_name param_count
%DELTAIL(I) mmac_name param_count

While the HEAD variants add/delete a line at the
beginning, the TAIL variants add/delete a line at
the end. Without a trailing I, the macro name is
matched case-sensitively; by contrast, with a
trailing I it is matched case-insensitively. The
parameter count has the same format as the one
used by %(I)MACRO. Last but not least, ADD adds a
new line (or empty line, if nothing is given),
while DEL deletes at line (or is ignored, if the
macro contains no more lines).

[nasm64developer]