Allow for the --parser option

[mrjoelkemp]

Allows the user to specify a particular version of jsdoc to use with JSDox. This avoids JSDox dictating the jsdoc version and having to maintain the dependency.

jsdox myFile --parser=path/to/my/jsdoc

• If --parser is not set, then check stdinput
• If no parser is supplied, either default to jsdoc3 (dynamically npm install) or use an internal parser?