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/lib/composure.bats

@@ -1,9 +1,9 @@
 #!/usr/bin/env bats
 
 load ../test_helper
-load ../../lib/composure
+load "${BASH_IT}/vendor/github.com/erichs/composure/composure.sh"
 
-@test "lib composure: composure_keywords()" {
-  run composure_keywords
+@test "lib composure: _composure_keywords()" {
+  run _composure_keywords
   assert_output "about author example group param version"
 }