add "hello_nim" example application written in Nim.

[centurysys]

Summary

Added sample application in Nim language

Impact

It allows you to create applications in the Nim language, which can be easily integrated with the C language so that you can use NuttX features in Nim right away.

1. No need to create HAL, binding modules.
2. Can use Nim standard libraries, external libraries.

Testing

Tested on sim, arm Cortex-A5, Cortex-M4.

1. install choosenim, latest Nim language.

https://nim-lang.org/install_unix.html
$ choosenim devel --latest

2. configure NuttX.

This example uses async/await, which requires the following items to be enabled

CONFIG_SCHED_CHILD_STATUS=y
CONFIG_NET=y
CONFIG_NET_SOCKOPTS=y

important:
I am sending out a pull request to clear Nim's asyncdispatch module global dispatcher at the end of the task.

nim-lang/Nim#21432

Until this accepted, the second and subsequent runs will fail.

[xiaoxiang781216]

Please fix the nxstyle error reported here:
https://github.com/apache/nuttx-apps/actions/runs/4272067879/jobs/7438598461

[centurysys]

@xiaoxiang781216
Regarding the second error, the function "NimMain()"(Fixed Name) must be called before calling the Nim process.
The name "NimMain" can be influenced via the --nimMainPrefix:prefix switch.
How should I correct this?

[xiaoxiang781216]

Fxing "Mixed case identifier found" is optional since the mixed case can't avoid completely in some context. Anyway, you can add NimMain to the white list here: https://github.com/apache/nuttx/blob/master/tools/nxstyle.c#L500

[centurysys]

Thank you very much.
I see that we need to make a change to add it to the whitelist of the repository on the nuttx OS side. Would you be willing to merge this one after I deal with that one?

[xiaoxiang781216]

Sure.

[centurysys]

Thank you for merging the changes on the OS side.
I have modified the style, is this correct?

[xiaoxiang781216]

Let's see the style check report.
BTW, you can run the check offline with:
../nuttx/tools/checkpatch.sh -g HEAD~...HEAD