add custom base directory support

Referring to issue #13

Added support like @bkuhl suggested. This will enable to execute command like ```blacksmith generate Foo.Foobar scaffold ~/path/to/config.json```. Also added a new template variable called ```{{Base}}``` to retrieve the base directory name

Signed-off-by: Ahmad Shah Hafizan Hamidin <ahmadshahhafizan@gmail.com>