Update README.md
Cache llvm/ directory
Refine the default llvm path for build script
Add default Dockerfile
Update Makefile.common.in default version to 3.4
Reset color after test cases
VERSION -> BuildMode for tests

Release+Debug+Asserts
Refine the Dockerfile and build scripts

Now you can run 'sudo docker build --rm -t giri .' to build the Docker
image with Giri and LLVM installed.
Add Docker image link
Refine the format
Purify the format

Trivial
Refine travis conf file according to ENV dependencies
Merge branch 'master' of github.com:liuml07/giri
Exit with test status
Refine the travis conf

Remove the branches target and add sudo to install llvm
Fix the bug of sudo -E to keep env
Change the default -j of install_llvm to 2

Perhaps we will run this script in local machines, Travis CI servers
and/or Docker hub servers. We do not want to eat up their CPU.
Only use GCC in Travis CI server

It seems that there is a bug of the clang installed in Travis CI.
Lacking of clang test is OK. Anyway, we build our LLVM by ourselves.
Let's suppose the world begins with NIL.
Add Travis CI badge to README

小崔说：本来Giri用户就少，如果一看build又error了，估计用户就更少了。
Merge branch 'master' of github.com:liuml07/giri