Changelog for weeder-0.1.3

Changelog for Weeder 0.1.3 #5, document how to install weeder #8, detect unused imports, even import Foo() #7, don't say modules with only instances are always redundant #6, don't give partial pattern matches when reading .weeder.yaml 0.1.2 #3, deal with space-separated hs-source-dirs 0.1.1 #2, use "stack query" rather than parsing stack.yaml 0.1 Initial version