Add '--mode' to set test coverage mode in cover.sh

Coverage mode options passed to 'go test'. Defaults to 'atomic'.
Run 'cover.sh --help' for usage. Ensure that results are in same dir
as cover.sh file.

cover.sh

diff --git a/cover.sh b/cover.sh
index 7c312e5..59dc9b4 100755
--- a/cover.sh
+++ b/cover.sh
@@ -1,10 +1,48 @@
 #!/usr/bin/env bash
 
 set -e
-echo "mode: atomic" > coverage.txt
 
+DIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
+
+usage()
+{
+cat << EOF
+Usage: $(basename $0) --mode CoverMode
+
+This script will run 'go test' on all non-vendor subdirs, then 'go tool cover'
+for test coverage. Any 'go test' failures will exit the script. If all tests
+are successful, it outputs a 'coverage.html' file with test coverage result.
+
+OPTIONS:
+ -h                 Show this message
+ -m or --mode       Test coverage mode: set, count, or atomic (default)
+EOF
+}
+
+# Set default variables
+coverMode="atomic"
+while :
+do
+    case $1 in
+        -h | --help | -\?)
+        usage
+        exit 0      # This not an error, User asked help. Don't do "exit 1"
+        ;;
+        -m | --mode)
+            coverMode=$2
+            shift 2
+            ;;
+        *)
+            break
+            ;;
+    esac
+done
+
+echo "mode: $coverMode" | tee coverage.txt
+
+cd $DIR
 for d in $(go list ./... | grep -v vendor); do
-    go test -coverprofile=profile.out -covermode=atomic $d
+    go test -coverprofile=profile.out -covermode=$coverMode $d
     if [ -f profile.out ]; then
         tail +2 profile.out >> coverage.txt
         rm profile.out