Updated the way built-in commands are called/used

Previously, built-in commands were fairly primitive, merely outputting
STDOUT and STDERR with the print! macros. However, we need them to
behave like normal programs, that is:

  - Acknowledge their verse's meter (forking, piping, etc.),
  - Ability to capture STDOUT and STDERR (>, 2>),
  - and Affect the currently running environment.

For these reasons, the anthology was reworked, and now contains the
Anthology struct, which mimics both std::process::{Child, Command}.

The AnthologyStdin helper struct was also created, for built-ins to
take input on STDIN, though no built-in is currently using it.

Each built-ins' incant functions were updated to return a
std::process::Output. It contains output from STDOUT, output from
STDERR, and the exit code of the "process".

A fix was also implemented for aliases, where the STDOUT and STDERR
vectors were not being copied to the newly constructed verse.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/compose/environment.rs b/src/compose/environment.rs
index ea6d070..18d59c4 100644
--- a/src/compose/environment.rs
+++ b/src/compose/environment.rs
@@ -24,6 +24,7 @@ use std::collections::HashMap;
 ///     ()
 /// }
 /// ```
+#[derive(Debug, PartialEq, Eq, Clone)]
 pub struct Environment {
     pub aliases: HashMap<String, String>,
     pub bins: Vec<String>,