Add documents for using JDK7 (#314, #323).
Add documents for using JDK7 (#314, #323).

akirakw/asakusafw,ashigeru/asakusafw,asakusafw/asakusafw,cocoatomo/asakusafw,cocoatomo/asakusafw,ashigeru/asakusafw,asakusafw/asakusafw,akirakw/asakusafw