Custom CodeRunner config settings per file or project

Although is possible to run custom commands, it would really useful if we can define settings per file and per directory/project
i.e. suppose we have inside a dir
```bash
foo.xxx
bar.xxx
```
now consider add two files like that
```bash
foo.coderunner
project.coderunner
```
where *.coderunner files contain some settings like
```json
{
"code-runner.customCommand": "echo Foo Special Settings"
}
```

```json
{
"code-runner.customCommand": "echo Project Special Settings"
}
```

Now if I run foo.xxx , CodeRunner will check if foo.coderunner exists and apply custom settings accordingly.
If I run bar.xxx , the check fails and it could failback checking if project.coderunner there exists.
If neither .codereunner nor project.coderunner exist then defaults settings are applied.

It would be very handy to switch python virtualenv, JDK version, etc,etc or even define peculiar workflows ( like the one requested in #370 )