Use of any JIRA field in a template

[switchtrue]

Currently the JIRAChangelogBuilder requires a command line argument of "--changelog-description-field " to be provided in order to specify field name in JIRA that provide the issue deescription.

Instead it would be good if you could just use any field name in the template and the changelog builder would fetch the appropriate fields from JIRA.

for example:
{{ summary }}
{{ fixVersion }}
{{ changelogdescription }}
{{ epiclink }}

There would have to be a deterministic policy on how tag names are related to field names (maybe case-insensitive and strip spaces?).

As this will involve the parsing of the templates to determine the field names it would also be good to introduce special place holders that can be replaced with environment variables, for example:

{{ $(SOME_ENV_VAR) }}

See if there is any functionality similar to this already in mustache (my gut feeling is no) and identify the "best way" to name the variables.