[FR] Special syntax for shim's directory / shim's target

[God-damnit-all]

There was progress made in #1 for this feature, and even some code reviewing done, but it seems to have stalled.

While %~dp0 is an option, I am bothered a bit by the fact that both % and ~ are allowed as part of filenames. Using characters that aren't allowed would be better.

My suggestion is <:/ /:> with a single-letter parameter in-between, as I feel that would be difficult to ever purposely put in as an argument for any other purpose.

---

Proposed syntax example

Shim executable: C:\Program Files (x86)\Example Directory\shim.exe

Desired Result	Syntax	Output
full path	<:/f/:>	C:\Program Files (x86)\Example Directory\shim.exe
directory	<:/d/:>	C:\Program Files (x86)\Example Directory
parent dir	<:/p/:>	C:\Program Files (x86)
child dir name	<:/c/:>	Example Directory
base name	<:/b/:>	shim
extension	<:/x/:>	.exe
name.ext	<:/n/:>	shim.exe

Prefixing the letter with a ! on the args = ‌ row would instead point to the path = ‌ path
e.g. using <:/!f/:> with path = cmd.exe would make <:/!f/:> resolve to C:\Windows\System32\cmd.exe

[God-damnit-all]

@kiennq I clarified the bit about the ! prefix at the bottom, since I think the way I worded it before was confusing.

[kiennq]

The ! requires us to find the full path for the launch cmd. I want to avoid that if possible as it can also imply security issues if we resolve to a wrong path.
Let me implement the <:/../:> first to see how it's going.