CLI: --var/--label: accept the usual int./floating point number form

CLI: --var/--label: accept the usual int./floating point number form

This patch makes the `--var` and `--label` options accept the usual
constant integer and floating point number (just for `--var`) forms of
the Normand language.

For example:

    --var=meow=-45.2e17
    --label=zoom=15ABh
    --var=mix=0b11010010

Also adding the `-v` short option for `--var` and accepting whitespaces
around the `=` of a `--var`/`--label` argument.

Change-Id: I3ecb1e85a68168e2304f550d48fdc6ccd447a706
Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Reviewed-on: https://review.lttng.org/c/normand/+/11018
Tested-by: jenkins <jenkins@lttng.org>