Various changes to address new 'bool' C23 type and preprocessor symbol clash

[mxmanghi]

various changes to address minor problems

• Rename configure.in as configure.ac as recommended by autotools
• Rename variable 'bool' into 'boolean (generic/yajltcl.c) since recent C32 compilers have introduced the type 'bool'
• Explicit definition of MODULE_SCOPE avoids preprocessor symbol clashing when compiling with Tcl9
• Undo INCLUDES symbol change that added the parent directory into the include directories list
• changing CONST definitions into regular C 'const' as prescribed by the Tcl9 transition guidelines. It's not hurting the build against Tcl8 but I'm not sure if it can have side effects

I opened this PR months ago but didn't get any reaction. Maybe Chris Roberts (@NasaGeek) may help?