Enhance some golo commands

**Enhancement of golo commands :**
- [x] `golo doc` support to parse folders and golo files
```sh
$ golo doc samples/
$
```
- [x] `golo diagnose` support to parse folders and golo files
```sh
$ golo diagnose samples/
$
```
- [x] `golo golo --files` parse folders to load golo files
- [x] `golo golo --module` is added to specify a Module name for the main function
```sh
$ golo golo --files samples/ --module hello.World
Hello World!
$ golo golo --files samples/ --module EchoArgs --args arg1 arg2
With a for loop and an index:
  #0 -> arg1
  #1 -> arg2
With a foreach loop:
  arg1
  arg2
With a foreach over a range:
  #0 -> arg1
  #1 -> arg2
$
```
- [x] add `--usage` option to golo command
```sh
$ golo --usage run
Runs compiled Golo code
Usage: run [options] Program arguments
  Options:
        --classpath
       Classpath elements (.jar and directories)
       Default: []
  *     --module
       The Golo module with a main function
$
````

**And**
- shell completion updated with `--module`
- add documentation for this enhancement
- rewrite some samples to have a new & unique module name (to avoid duplication in classpath)
Do we really need to silently discard non-`.golo` files?