Add benchSite.sh

And change site benchmark separator to comma to make it Bash and regexp friendly, example:

./benchSite.sh "frontmatter=YAML,num_root_sections=1,num_pages=.*,tags_per_page=20,shortcodes=false,render=false"

benchSite.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+
+# Send in a regexp mathing the benchmarks you want to run, i.e. './benchSite.sh "frontmatter=YAML"'. 
+# Note the quotes, which will be needed for more complex expressions.
+# The above will run all variations, but only for front matter YAML.
+
+echo "Running with BenchmarkSiteBuilding/${1}"
+
+go test -run="NONE" -bench="BenchmarkSiteBuilding/${1}" -test.benchmem=true ./hugolib