feat: support evaluated `rspfile` in `command`

[hikerpig]

I hacked some code to fix my issue #119 and managed to build my local project using n2.

I'm not familiar with Rust and ninja, so my implementation may be far from suitable, but still I want to open this PR to fill in some unittest of the issue and hopefully someone with a better understanding of this project can make it right both in performance and extendability.

[Colecf]

In ninja, the variable lookup is recursive, and has cycle detection, which is missing from this PR.

[hikerpig]

@Colecf Thank you for the direction, I can try to dig in ninja's code and port enough related feature and unit tests in my spare time.