Getting Bash-it to use the vendored composure

Fixed tests
Fixed install.sh and bash_it.sh
Added gitattributes to the vendor folder
Changed documentation

test/plugins/base.plugin.bats

@@ -1,7 +1,7 @@
 #!/usr/bin/env bats
 
 load ../test_helper
-load ../../lib/composure
+load "${BASH_IT}/vendor/github.com/erichs/composure/composure.sh"
 load ../../plugins/available/base.plugin
 
 @test 'plugins base: ips()' {