maint: add missing NEWS items since release v13.

* NEWS: Note change of treatment of underscores in example
descriptions.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
specl: use bold rather than bright white for lua errors.

* lib/specl/color.lua (colormap): Use bold attribute for strong
markup.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
specl: diagnose missing luaposix during argument parsing.

* lib/specl/util.lua (files): Return an error when luaposix was
required but missing.
* lib/specl/main.lua (execute): Display any error returned from
util.files.
* NEWS: Update.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
inprocess: break an infinite loop in env.io.type.

* lib/specl/inprocess.lua (env_init): Inside the type method,
get the `_type` value directly from the metatable instead of
calling std.object.type, which in turn may call back into the
env.io.type method.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
maint: update to stdlib >= 41.

* lib/specl/std.lua (init, std.string.require_version)
(std.list.elems): Refactor from these...
(_DEBUG, std.require, std.ielems): ...to these.
(std.functional.bind, std.io.dirname, std.table.len): Remove
overrides, allow use of exported versions of the same.
* rockspec.conf (dependencies): Bump stdlib requirement to >= 41.
* specl-git-1.rockspec: Regenerate.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
maint: std.object >= v41 do not support __totable metamethods.

* lib/specl/matchers.lua (totable): A compatibility function
over new std.pairs implementation.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
maint: std.string.tostring is deprecated by stdlib 41.

* lib/specl/match.lua (tostring): Import std.tostring instead of
deprecated std.string.tostring.
* lib/specl/util.lua (concat): Likewise.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
refactor: use std.functional.map and remove specl.util.map.

* lib/specl/util (map): Remove.
Adjust all callers and simplify accordingly.
(examplename): Factor out this common call sequence into a
utility function.
Adjust all client code, and simplify accordingly.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
refactor: use pure lambda strings to simplify specl.std.

* lib/specl/std.lua (M): Use the new std.operator.set to
load std submodules into specl.std table using only pure lambda
functions.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
specs: update bit-rotted error messages.

* specs/spec_helper.lua (spawn_specl, run_spec): Use the correct
function name for error messages.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
matchers: import std.getmetamethod before use.

* lib/specl/matchers.lua: stdlib >= 41 no longer monkey patches
the global table with a getmetamethod function, so import it
explicitly from std.

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