[Fixes Issue #12] Changed MapSetter parser

The MapSetter class now correctly deals with multiple '=' signs being 
present in the value part. This changes the behaviour as follows:

Input: "foo=bar=baz"
Old (key, value): ("foo", "bar")
New (key, value): ("foo", "bar=baz")

Converted mixed indentation to only-tabs.
Added copyright statement and MIT licence text.

Fixes: https://github.com/kohsuke/args4j/issues/12
Signed-off-by: Martin Schroeder <martin.h.schroeder@intel.com>