build, check, test the new R package

[stevenhwu]

Have a look at the README.md, there are some basic usage of the r package,
including in R, using check(), test() to validate the package

• Currently, there are some warnings, we can deal with them later as part of the code convention.
• Update these test cases.

using load_all() to load this R package without installing it. This enables to you run simulations and build new features in this package.