[Feature] access compile time environment variables

[b1ek]

Is your feature request related to a problem? Please describe.
see #431

Describe the solution you'd like
i think that we should add rust-like compile time macros, like env!() in this case which should enable the user to access compile time environment variables.

for the env!() macro, i suggest the following syntax:

fun env(variable: Text, default: Text): Text {
    // returns the specified variable if it exists, and default if it is set and the env variable is not available.
    // if default value is not set and variable is not available, it will throw a compile time error
}

which should be used like this:

const compile_commit = env!("COMPILE_COMMIT", "unknown");

which should be compiled to something like this (assuming COMPILE_COMMIT is set to a8c3083f:

declare -r compile_commit = "a8c3083f"

Describe alternatives you've considered
#431 (comment)

[Mte90]

IF those are compiler variables I think that env can be confusing with the env functions we have in stdlib.
Maybe compiler_env is better.

[b1ek]

IF those are compiler variables I think that env can be confusing with the env functions we have in stdlib. Maybe compiler_env is better.

yeah, i think that would work too. i suggested env!() because it is the same that rust has