maint: The Grand Renaming™ - use `require "std.list"` etc.

* Makefile.am (SPEC_ENV, SPECL, SPECL_MIN, SPECS, MULTICHECK)
(check-local, src_spec): Split out from here...
* specs/specs.mk (SPECL_ENV, SPECL, SPECL_MIN, specl_SPECS)
(MULTICHECK, specs-check-local, std_path): New file.  ...to here.
* Makefile.am (SOURCES, dist_data_DATA, dist_doc_DATA)
(dist_files_DATA, dist_modules_DATA): Split out from here...
* std/std.mk (nobase_dist_lua_DATA, dist_lua_DATA, std/std.lua)
(dist_doc_DATA, dist_files_DATA, dist_modules_DATA): New file.
...to here.
* specs/debug_ext_spec.yaml, specs/getopt_spec.yaml,
specs/io_ext_spec.yaml, specs/math_ext_spec.yaml,
specs/package_ext_spec.yaml, specs/string_ext_spec.yaml,
specs/table_ext_spec.yaml: Adjust require calls.
* src/base.lua, src/bin.lua, src/debug_ext.lua, src/debug_init.lua,
src/fstable.lua, src/getopt.lua, src/io_ext.lua, src/lcs.lua,
src/list.lua, src/math_ext.lua, src/mbox.lua, src/modules.lua,
src/object.lua, src/package_ext.lua, src/parser.lua, src/set.lua,
src/std.lua.in, src/strbuf.lua, src/strict.lua, src/string_ext.lua,
src/table_ext.lua, src/tree.lua, src/xml.lua: Move from here...
* std/base.lua, std/bin.lua, std/debug_ext.lua, std/debug_init.lua,
std/fstable.lua, std/getopt.lua, std/io_ext.lua, std/lcs.lua,
std/list.lua, std/math_ext.lua, std/mbox.lua, std/modules.lua,
std/object.lua, std/package_ext.lua, std/parser.lua, std/set.lua,
std/std.lua.in, std/strbuf.lua, std/strict.lua, std/string_ext.lua,
std/table_ext.lua, std/tree.lua, std/xml.lua: ...to here. Adjust
require calls.
* std/modules.lua: Add "std." prefix.
* std/std.lua.in: Strip "std." prefix before injecting required
symbols into global namespace.