add function to get real configure file's path

The function getFilePath is to get real config path. It solves a problem that if the configuration file had a password or other important thing, and worried about other people see it in the file after we sharing in the project.

We can use like:
export ProjectName_config="a.config=/.../a.config;b=/.../b.config",
getFilePath("a.config") return "/.../a.config", and
if export ProjectName_config="" or not, we use local configuration file: a.config.

such as:
export test_config="test.config=$HOME/test.config"
export test_config="test.config=$HOME/test.config;test2.config=$HOME/test2.config"
export test_config=""