Squashed 'extenal/shmdb/' changes from ff41309..3113061

3113061 use log API to print log to console. Add the test case of child process write data and parent process read.

git-subtree-dir: extenal/shmdb
git-subtree-split: 3113061a1dd2f1a08f1e32aff2436fe117bc4e75
Merge commit 'c571c078b7b2e2282a3fb9b964628e67d6dea2c5'
add test case.
reconstruction the constructor of Shmdb.
reconstruction the log function
add stdlib.h
add package.json and readme.md.