maint: update sets to use lua 5.2 style modules.

This is backwards compatible with lua 5.1, and allows use of sets
with the strict module loaded, which raised a bogus error before.
* src/std.lua.in (version): Return this in the module namespace.
Require the bundle of "std" modules into the global namespace.
* src/set.lua: Declare everything locally, and return a table
of interfaces, per lua 5.2 module style.
maint: update lists to use lua 5.2 style modules.

* src/list.lua: Declare everything locally, and return a table of
interfaces, per lua 5.2 module style.
Adjust all callers.
maint: update trees to lua 5.2 style modules.

* src/tree.lua: Declare everything locally, and return a table of
interfaces, per lua 5.2 module style.
maint: update bin to use lua 5.2 style modules.

* src/bin.lua: Declare everything locally, and return a table of
interfaces, per lua 5.2 module style.
maint: update fstable to use lua 5.2 style modules.

* src/fstable.lua: Declare everything locally, and return a table
of interfaces, per lua 5.2 module style.
maint: update getopt to use lua 5.2 style modules.

* src/getopt.lua: Declare everything locally, and return a table
of interfaces, per lua 5.2 module style.
maint: update lcs to use lua 5.2 style modules.

* src/lcs.lua: Declare longestCommonSubseq locally, and return a
table containing a reference to it, per lua 5.2 module style.
maint: update mbox to use lua 5.2 style modules.

* src/mbox.lua: Declare parse locally, and return a table with a
reference, per lua 5.2 module style.
maint: update setbuf to use lua 5.2 style modules.

* src/strbuf.lua: Declare everything locally, and return a table
of interfaces, per lua 5.2 module style.
Adjust all callers.
maint: update object to use lua 5.2 style modules.

* src/object.lua: Simply return the callable Object table.
Adjust all callers.
maint: update parser to use lua 5.2 style modules.

* src/parser.lua: Simply return the Parser object.
Merge branch 'pull-request/move-to-lua52-module-style' into next