add: support for Makefile (simplified)

[metaist]

Thanks to @jhostyk for pushing me to support a simplified Makefile format.

Current example: https://github.com/metaist/ds/blob/main/examples/formats/Makefile

• treat all targets as .PHONY:
• handle 1 target name (hold off on multiple targets or repeating the target multiple times)
• multiple prerequisites
• first line of recipe on the same line
• handle line continuations outside of recipe
• handle line continuations inside the recipe (hold off on .POSIX: for now)
• treat the recipe as one big lump you send to the shell
• (NONSTANDARD) handle error suppression (-) in any line of the recipe
• (NONSTANDARD) handle error suppression (-) in any prerequisite name
• (NONSTANDARD) read comment on target definition line as description
• $@ name of the target
• $< first prerequisite (not supported: archive)
• $? all prerequisites (not supported: "newer than target")
• $^ all prerequisites only once

[metaist]

The idea of grabbing the comment on the same line as the targets is clever, but maybe too clever. .json files don't get a comment, so Makefile probably shouldn't either.

[metaist]

The example they have documents it as such: https://www.gnu.org/software/make/manual/make.html#Rule-Example

Going to put it back in.

[metaist]

https://github.com/metaist/ds/actions/runs/10501662150/job/29092020291

[metaist]

If I ever want to implement more, Chris Wellons has some reasonable suggestions:
https://nullprogram.com/blog/2017/08/20/

[metaist]

After #77, we can actually use _.env as a place to store common env which we want to add to all recipes.