specl: formatters report file:line:expectation in verbose output.

* specs/formatter/report_spec.yaml: Add specifications for
desired improved output in verbose mode.
* lib/specl/loader.lua (parser_mt:load_map): Save line number
* into map table value when a Lua function is loaded.
* lib/main.lua (slurp): Save filenames into specs table from
loader.
* lib/specl.lua (filename): New file local variable to hold the
most recently encountered specs table filename.
(run): Set filename at each iteration.
(run_examples): Adjust for changes in example table layout.
Pass filename and line number to formatter.expectations().
* lib/specl/formatter/progress.lua (expectations): Report file:
line:expectation in verbose output for pending and failed
examples.
* lib/specl/formatter/report.lua (expectations): Likewise.
* doc/specl.md: Update.
* NEWS: Update.

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