[clone] update README, improve delegate docs

Author: Byron

README.md

@@ -100,17 +100,19 @@ Please see _'Development Status'_ for a listing of all crates and their capabili
   * [ ] API documentation with examples
 
 ### git-protocol
+  * _abstract over protocol versions to allow delegates to deal only with a single way of doing things_
   * [x] **credentials**
     * [x] via git-credentials
     * [ ] via pure Rust implementation if no git is installed
   * [ ] fetch & clone
     * [x] control credentials provider to fill, approve and reject
-    * [x] ls-ref
+    * [x] command: ls-ref
       * [x] parse V1 refs as provided during handshake
       * [x] parse V2 refs
     * [x] initialize and validate command arguments and features sanely
+    * [x] abort early for ls-remote capabilities
+    * [ ] packfile negotiation
   * [ ] push
-  * [ ] shallow clones
   * [ ] API documentation with examples
 
 ### git-packetline

git-protocol/src/fetch/delegate.rs

@@ -13,7 +13,7 @@ pub enum Action {
 
 pub trait Delegate {
     /// Called before invoking ls-refs to allow providing it with additional `arguments` and to enable `features`.
-    /// Note that some arguments are preset based on typical usage.
+    /// Note that some arguments are preset based on typical use, and `features` are preset to maximize options.
     /// The `server` capabilities can be used to see which additional capabilities the server supports as per the handshake.
     /// Note that this is called only if we are using protocol version 2.
     fn prepare_ls_refs(
@@ -24,7 +24,8 @@ pub trait Delegate {
     ) {
     }
 
-    /// Called before invoking the 'fetch' interaction, with `arguments` and `features` pre-filled for typical use.
+    /// Called before invoking the 'fetch' interaction, with `features` pre-filled for typical use
+    /// and to maximize capabilities.
     /// `refs` is a list of known references on the remote, based on the handshake or a prior call to ls_refs.
     /// As there will be another call allowing to post arguments conveniently in the correct format, i.e. `want hex-oid`,
     /// there is no way to set arguments at this time.

git-protocol/src/fetch/mod.rs

@@ -129,6 +129,8 @@ pub fn fetch<F: FnMut(credentials::Action) -> credentials::Result>(
         transport.close()?;
         return Ok(());
     }
+    let mut _fetch_arguments = Command::Fetch.initial_arguments(&fetch_features);
+    // TODO: negotiation rounds till pack file is received or someone aborts.
 
     transport.close()?;
     unimplemented!("rest of fetch or clone")

git-transport/src/client/capabilities.rs

@@ -29,7 +29,7 @@ quick_error! {
     }
 }
 
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub struct Capabilities {
     data: BString,
     value_sep: u8,