Additional documentation for test scripts

Added documentation in comments in test scripts, added example site.sh,
moved evaluation of site.sh later in lib.sh to allow site.sh to override
more lib.sh variables.

test/sum.sh

@@ -1,15 +1,30 @@
 #!/usr/bin/env bash
-# Run, eg as:
-# ./sum.sh # to run all tests and print 
+# Run test_*.sh tests, continue on error, no logging, print pass/fail summary.
+#
+# This script requires the user to be in the sudo group.
+#
+# The 'pattern' variable determines which test files are executed.
+# By default, run all the tests in the test_*.sh files in this directory.
 
+: ${pattern:=test_*.sh}
+
+# You can specify tests files to exclude using the 'SKIPLIST' variable in a
+# site.sh file. See example in README.md. Files excluded by the 'SKIPLIST'
+# variable have precedence over files included by the 'pattern' variable.
+
+# This script does not take arguments, so if arguments exist, print the Usage
+# in http://docopt.org/ format.
 if [ $# -gt 0 ]; then 
-    echo "usage: $0 # pipe to dev/null and continue on error"
+    echo "Usage:"
+    echo "    ${0}                             # Run all 'test_*.sh' files"
+    echo "    pattern=<Bash glob pattern> ${0} # Run only files matching the pattern"
+    echo ""
+    echo "Example:"
+    echo "    ${0} 2>&1 | tee test.log         # Run all tests, output to 'test.log'"
+    echo "    pattern=test_feature.sh ${0}     # Run only the tests in 'test_feature.sh'"
     exit -1
 fi
 
-# Pattern to run tests, default is all, but you may want to narrow it down
-: ${pattern:=test_*.sh}
-
 err=0
 for testfile in $pattern; do # For lib.sh the variable must be called testfile
     echo "Running $testfile"