add more checks for programs and headers

    $ autoscan  # e93271589ad6fb350809745e75a14e2e5514d3bf
    configure.ac: warning: missing AC_PROG_CXX wanted by: build-aux/ltmain.sh:960
    configure.ac: warning: missing AC_PROG_RANLIB wanted by: build-aux/ltmain.sh:2455

autoscan gave two warnings, the former  isfor C++, doesn't seem to be actually needed; the latter is obsolete:

    libtoolize: `AC_PROG_RANLIB' is rendered obsolete by `LT_INIT'

The generated configure.scan has

    AC_CONFIG_SRCDIR([config.h.in])

The current checks for src/main.c, it should also does the job.
bring back testsuite.at to include testsuites, use macro to run same tests on both td and td.sh
fix only "0 seconds" is printed when duration is 0 and print_all_number is true, test accordingly
add --disable-bash and --disable-c to configure; install, tests (Check and Autotest), benchmark skip disabled implementation
update instruction for Git installation
output configured summary
make Check unittest optional