Add an option to cargo-espflash to flash file without having to build the project

[SergioGasquez]

Maybe, if we have an argument pointing to an elf file, flash it instead of building the project and then flashing the resulting file.

[MabezDev]

This is what espflash does already! Easy to confuse with cargo-espflash which is the cargo wrapper that also builds the project. They are actually two different executables.

[SergioGasquez]

Sorry, I meant cargo-espflash. My point was to get this feature inside cargo-espflash so users that want to flash a file without building the project do not need to install espflash or rely on idf tool.

[tcbennun]

Agreed on this. It actually can cause a rebuild in some cases (e.g. performing a workspace build then using cargo espflash to flash one of the binary crates).

[MabezDev]

I believe this was closed via #205

[jessebraham]

This was closed erroneously, re-opening.

[jessebraham]

After thinking on this for awhile, I actually think it's not necessary. If the project is already built then normal execution is fine, the time added by rustc for an already built project is negligible.