Use GNU grep, sed and awk instead of BSD variants. Developers will have
to install these using a package manager like homebrew. Updated the
INSTALL.md and doc/Development.md tech docs with instructions.
Henceforward, aclocal.m4 will be generated by the 'autoreconf' command.
The 'autoreconf -f -i' command may now emit a warning "Unsupported
attribute section, the test may fail" on some systems, but it will still
generate the proper aclocal.m4 and ./configure files. To suppress this
warning, simply invoke autoreconf with '-I m4' argument:
autoreconf -f -i -I m4
The INSTALL.md has been updated accordingly, and a new 'Notes for
Developers' technical document added, explaining the use of aclocal and
autoreconf, and documenting that these warning messages are of no
concern.
