Added 'bool' support to user editable parameters
The parameter will be displayed as checkbox in the generated form.
For default values of type other than boolean an error will be displayed.
In the user script the value can be used as boolean.

example:
{ name: 'check', caption: 'awesome?', type: 'bool', default: true }
Added 'longtext' support to user editable parameters
The parameter will be displayed as textarea in the generated form.

example:
{ name: 'multilineText', caption: 'Long text:', type: 'longtext', default: "long\ntext\nis\nlong" }
Added parameter definition 'visible' to user editable parameters.
if set to false the parameter will not be exposed, but still be useable for the script (i.e. it's default value)

example:
{ name: 'resolution', caption: 'Resolution:', type: 'int', default: 20, visible: false }
Merge pull request #29 from v01pe/additional_types

Additional types for user editable parameters