Add bash-it search functionality

- "bash-it search term1 [term2]...."

 - we are using existing 'bash-it show plugins|aliases|completions'
   commands output, to search (with grep) for lines that match the
   search terms, and then output the matches.

 - wrote a simple unit test that for whatever reason fails on Travis,
   so wrapped it in 'if "Darwin"'...

test/lib/helpers.bats

@@ -0,0 +1,19 @@
+#!/usr/bin/env bats
+
+load ../../lib/composure
+load ../../plugins/available/base.plugin
+
+cite _about _param _example _group _author _version
+
+load ../../lib/helpers
+
+NO_COLOR=true
+IS_DARWIN=false
+[[ "$(uname -s)" == "Darwin" ]] && IS_DARWIN=true
+
+if [ "$IS_DARWIN" == "true" ]; then
+  @test "helpers search aliases" {
+    run _bash-it-search-component 'plugins' 'base'
+    [[ "${lines[0]}" =~ 'plugins' && "${lines[0]}" =~ 'base' ]]
+  }
+fi

test/run

@@ -1,4 +1,6 @@
 #!/usr/bin/env bash
+PATH=$PATH:$(pwd)/bats/bin
+set +e
+[[ -z "$(which bats)" ]] && git clone --depth 1 https://github.com/sstephenson/bats.git
 set -e
-
 exec bats ${CI:+--tap} test/{lib,plugins}