Add release scripts (#256)

- Add release note generator
- Move update version to scripts/

Author: rogebrd

scripts/release_note_generator.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+
+last_version=$(git tag --sort v:refname | tail -n 2 | head -n 1)
+echo "Getting commit history since $last_version"
+num_commits=$(git rev-list --count $last_version..HEAD)
+echo "Found $num_commits commits since last revision"
+git_log=$(git log -n $num_commits --pretty="format:* %s %n")
+linked_log=$(echo "Release Notes: \n\n$git_log" | sed -e 's/#\([0-9]*\)/[#\1](github.com\/dropbox\/dropbox-sdk-python\/pull\/\1)/g')
+echo "\n\n$linked_log"