Add template options.

[vexorian]

As decided in #93.

This adds an optional "options" field to a template's section in config file.

Then we can do:

options {
     key = value
}

After that, when the template is rendered, we can call ${Options.key} to render it and also do ${if Options.key} which will return false if the key is null or evaluates to "false" and true otherwise.

[zen0wu]

If you think it's necessary, we can upgrade the version of the config library.

[vexorian]

@shivawu it seems to work fine with the workaround.

@wookayin: I used HashMap because that's what the language section used. Why would Map be better?