configury: support non-autotool LuaRocks installation.

* Makefile.am, build-aux/mkrockspecs, build-aux/rockspecs.mk:
Sync with upstream slingshot.
* src/specl.in: Move from here...
* lib/specl.in: ...to here.
* configure.ac (SPECL_FALSE): Adjust.
(AC_CONFIG_FILES): Generate a non-writeable bin/specl from
lib/specl.in.
(AM_INIT_AUTOMAKE): Remove `foreign` option, so
that INSTALL is distributed, among other small nits.
* lib/specl.in (@LUA@): Remove substituted value, and replace
with a Bourne shell Lua search, and use that to re-execute.
(package.path): Do not set here.
* specs/specs.mk (specs/specl): Generate a wrapper to set
LUA_PATH appropriately for running bin/specl in the build tree.
(SPECL): Use it.
* specs/specl_helper.lua (run_spec): Use it.
* bootstrap: Create a README softlink to keep Automake happy.
* src/.gitignore, src/specl.lua, specl/color.lua,
specl/formatter/progress.lua, specl/formatter/report.lua,
specl/formatter/tap.lua, specl/matchers.lua, specl/optparse.lua,
specl/shell.lua, specl/std.lua, specl/util.lua: Move from
here...
* bin/.gitignore, lib/specl.lua, lib/specl/color.lua,
lib/specl/formatter/progress.lua, lib/specl/formatter/report.lua,
lib/specl/formatter/tap.lua, lib/specl/matchers.lua,
lib/specl/optparse.lua, lib/specl/shell.lua, lib/specl/std.lua,
lib/specl/util.lua: ...to here.
* src/src.mk, specl/specl.mk: Consolidate into...
* local.mk: ...here.
* m4/.gitignore, specl/.gitignore, specs/.gitignore: Delete.
* rockspec.conf (build.copy_directories): Add docs and bin.
* NEWS, README.md: Update.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>