build.rs is misused and invoked on any change to sources

[murlakatamenka]

Current build.rs is misused and slows down iteration time, because it only builds docs and doesn't need to run on any change to sources.

In my case, for around ~3 seconds while I work on #95 and #100

Solutions are well known:

• rerun-if-changed for docs/*.scd files
• or to use environment variable to trigger building man pages:

// build.rs
fn main() {
    if std::env::var("BUILD_DOCS").is_err() {
        std::process::exit(0);
    }

    // build docs if env var is set
}

BUILD_DOCS=1 cargo build --release

[Shinyzenith]

Hi this has been fixed in our dev branch thanks to @murlakatamenka . Will land in main branch soon.