cocoa_bridge: Continue outline of Objective C callable

Add some more structure to the function that will be called from
Objective C code.

* Give it a name, `parse_mappings` (not very thoroughly considered)
* Initialise some Foundation data structures to mirror our Rust ones
* Add the beginning of a struct that will be the ObjC version of our
  `MapGroup` struct, containing `NSDictionary`ies.
* Move the `extern crate` into `lib.rs`, I keep forgetting that's where
  they go.
* Add a test that just calls `parse_mappings` to check that the code
  compiles.

parser::MapGroup:
Make both its fields public to enable us to access them from
`cocoa_bridge`.

Used this helpful example as a reference for the Rust Cocoa code:
https://github.com/servo/core-foundation-rs/blob/c99c05c/cocoa/examples/hello_world.rs

1 files changed, 2 insertions, 2 deletions

diff --git a/src/parser.rs b/src/parser.rs
index a34edff..d5cd860 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -51,8 +51,8 @@ struct Mode {
 
 #[derive(Debug, PartialEq)]
 pub struct MapGroup {
-    maps: MapCollection,
-    modes: HashMap<Trigger, MapCollection>,
+    pub maps: MapCollection,
+    pub modes: HashMap<Trigger, MapCollection>,
 }
 
 #[derive(Debug, PartialEq)]