Add CI support for panic detection

panic-test.sh script under .traivs dir detect panic/unwrap calls, which
will panic the thread and cause process abortion.

.travis.yml

@@ -7,3 +7,4 @@ script:
     - cargo fmt --all -- --check
     - cargo build
     - cargo test
+    - bash ./.travis/panic-test.sh ./.travis/banned_function.txt

.travis/banned_function.txt

@@ -0,0 +1,2 @@
+unwrap()
+panic!(.*)

.travis/panic-test.sh

@@ -0,0 +1,37 @@
+#!/bin/bash
+
+# Check the unwrap and panic function presenting in src/ directory
+# of the repo. Testing suite is excluded. If such a function presents
+# return exit 1 for fail, otherwise return exit 0 for sucess.
+
+# Getting the banned list from banned functions
+banned_list=()
+banned_function="$1"
+while read -r line; do
+    banned_list=(${banned_list[@]} "$line")
+done < "$banned_function"
+
+output=""
+catch_panic=$false
+
+# Match panic call based on the given banned funciton list
+for i in src/*; do
+    for func in "${banned_list[@]}"; do
+	    tmp_line=$(sed '/#\[cfg(test)]/q' $i | grep -e "$func" | awk 'END {print NR}')
+        if [ "$tmp_line" -gt 0 ]; then
+            tmp_output=$(sed '/#\[cfg(test)]/q' $i | grep -n -e "$func")
+            output="${output}${tmp_output}\n"
+	    catch_panic=$true
+        fi
+    done
+done
+
+# Output result
+if [ $catch_panic ]; then
+    echo "exit 1. Please removed all the following panic calls."
+    printf "$output"
+    exit 1
+else
+    echo "exit 0. Not panic violation occurs."
+    exit 0
+fi