parameter templates and job environment

[hjoliver]

We should document more clearly that use of `parameter templates' changes the formatting of the parameter for use in task names, but it does not change the value of the parameter.

For example, if parameter m is an integer templated as %(03)s then foo<m> for m=3 becomes foo003 but in the job environment $CYLC_TASK_PARAM_m is just 3, not 003.

If the job needs the formatted value too, options are:

[runtime]
  [[foo<m>]]
    [[[environment]]]
       M1 = $(printf "%03d" $CYLC_TASK_PARAM_m)  # "003"
       M2 = %(m)03d  # "003"