Add release script (#54)

* Add release script

Release process:
1. Change version number in build.gradle
2. Execute ./release.sh

* bugfix

1. Fetch all tags from upstream first
2. Fix the case of the first rc version

find_version.py

@@ -0,0 +1,10 @@
+#!/usr/local/bin/python
+import re
+
+with open("build.gradle", "r") as f:
+	l = f.read()
+	m = re.search("allprojects\s+{\s+version\s+(.*)\s", l)
+	versionString = m.group(1)
+	versionString = versionString[1:]
+	versionString = versionString[:-1]
+	print versionString

release.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+
+# Fetch tags from upstream first
+git fetch -t git@github.com:klaytn/caver-java.git
+
+VERSION=$(./find_version.py)
+echo "Trying to tag v$VERSION"
+git tag | grep "$VERSION\$"
+if [ $? -eq 0 ]; then
+  echo "$VERSION is found in git tag!!! You should upgrade version number first!!!"
+  echo "Exiting..."
+  exit 1
+fi
+
+PREV_RCVERSION_FULL=`git tag | grep "$VERSION" | sort | tail -1`
+RCSUFFIX="1"
+if [ ! -z "$PREV_RCVERSION_FULL" ]; then
+  RCSUFFIX=$(echo "${PREV_RCVERSION_FULL##*.}"+1 | bc)
+fi
+
+RCVERSION="v$VERSION-rc.$RCSUFFIX"
+echo "tagging $RCVERSION"
+
+git tag $RCVERSION
+git push upstream $RCVERSION