Add `NotmuchEnum` trait and `notmuch_enum!` macro.

Implements enum types in pairs, specifying the type and variant names of
each, like so:

    notmuch_enum! {
        pub enum enum_name => EnumName {
            variant_one => VariantOne,
            variant_two => VariantTwo
        }
    }

Which expands to:

    pub enum enum_name {
        variant_one,
        variant_two
    }

    pub enum EnumName {
        VariantOne,
        VariantTwo
    }

The `NotmuchEnum` trait also entails two functions to convert between
the defined pairs, `from_notmuch_t()` and `to_notmuch_t()`.  The macro
takes care of their implementation, also.

Yes, this is purely aesthetic whimsy:  I wanted the types in the `ffi`
module to match the types from the `notmuch.h` file, and I wanted the
types I used within (and exported by) this crate to match the expected
Rust convention.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/lib.rs b/src/lib.rs
index 5c2fbd6..0f88f60 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,4 +1,8 @@
 #![feature(libc)]
 extern crate libc;
 
+#[macro_use]
+mod macros;
+
 mod ffi;
+mod utils;