#102 add support for __INVOKE__

[nasm64developer]

In my local forked version I have added support for
invoking a
multi-line macro in a way where the invocation gets
replaced
by an explicit return value, i.e. a token list.

The original idea/implementation came from Nickolay (unv).

Attached you can find a cleaned up version.

[nasm64developer]

changes needed to add INVOKE support

[nasm64developer]

getline() split into 3 components, and invoke_mmacro() cloned from it

[nasm64developer]

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Fwiw, adding support for invoking a multi-line
macro will expose NASM's left-to-right grouping
of "? and :" operators (see SF RFE #758548) --
which is unlike C's right-to-left grouping.

[nasm64developer]

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The first of the two fclose(i->fp) calls
in invoke_mmacro() needs to be guarded by
a NULL pointer check. (Some platforms do
silently ignore fclose(NULL) but others
cause trouble. For example, I got a bunch
of "segmentation fault" errors in Linux,
while Cygwin worked fine.)

[nasm64developer]

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The second of the two fclose(i->fp) calls
in invoke_mmacro() needs to be guarded by
a NULL pointer check too.