Replace ad-hoc build logic with cargo-near

[itegulov]

I think the existing cargo build logic can be replaced with cargo-near's public API (apart from being a CLI tool it also comes as a library). Less things to maintain => more better?

[ChaoticTempest]

wouldn't this require users to install cargo-near themselves first? I guess we can add it to build.rs script, but can it be used directly as a rust library?

[itegulov]

Yeah, it has a lib.rs, so it should be possible to use it directly as a regular library. The API might be awkward though, we haven't paid much attention to its "cli-as-a-library" design.

[ChaoticTempest]

This should also alleviate the error message problem when unable to compile with cargo build shown in #236

[ghimire007]

@frol As per our offline discussion, I would like work in this issue.