A simple loader that looks only in the directory(ies) you
specify in the ctor, but it uses the classpath rather than
absolute dirs so it can be used when the ST application is jar'd up.
You may specify the char encoding.
Pass a single dir or multiple dirs separated by colons from which
to load groups/interfaces. These are interpreted as relative
paths to be used with CLASSPATH to locate groups. E.g.,
If you pass in "org/antlr/codegen/templates" and ask to load
group "foo" it will try to load via classpath as
Look in each relative directory for the file called 'name'.
Load via classpath.
String fileName = dir+"/"+name;