Restructure modules

Modules are now separated into a fashion where the library can be used
for most use cases, without needing to compile the rest.

The core of serenity, with no features enabled, contains only the
struct (model) definitions, constants, and prelude. Models do not have
most functions compiled in, as that is separated into the `model`
feature.

The `client` module has been split into 3 modules: `client`, `gateway`,
and `http`.

`http` contains functions to interact with the REST API. `gateway`
contains the Shard to interact with the gateway, requiring `http` for
retrieving the gateway URL. `client` requires both of the other features
and acts as an abstracted interface over both the gateway and REST APIs,
handling the event loop.

The `builder` module has been separated from `utils`, and can now be
optionally compiled in. It and the `http` feature are required by the
`model` feature due to a large number of methods requiring access to
them.

`utils` now contains a number of utilities, such as the Colour struct, the
`MessageBuilder`, and mention parsing functions.

Each of the original `ext` modules are still featured, with `cache` not
requiring any feature to be enabled, `framework` requiring the `client`,
`model`, and `utils`, and `voice` requiring `gateway`.

In total the features and their requirements are:

- `builder`: none
- `cache`: none
- `client`: `gateway`, `http`
- `framework`: `client`, `model`, `utils`
- `gateway`: `http`
- `http`: none
- `model`: `builder`, `http`
- `utils`: none
- `voice`: `gateway`

The default features are `builder`, `cache`, `client`, `framework`,
`gateway`, `model`, `http`, and `utils`.

To help with forwards compatibility, modules have been re-exported from
their original locations.

1 files changed, 35 insertions, 0 deletions

diff --git a/src/http/error.rs b/src/http/error.rs
new file mode 100644
index 0000000..8e68c44
--- /dev/null
+++ b/src/http/error.rs
@@ -0,0 +1,35 @@
+use hyper::status::StatusCode;
+use std::error::Error as StdError;
+use std::fmt::{Display, Formatter, Result as FmtResult};
+
+#[derive(Clone, Debug, Eq, Hash, PartialEq)]
+pub enum Error {
+    /// When a status code was unexpectedly received for a request's status.
+    InvalidRequest(StatusCode),
+    /// When the decoding of a ratelimit header could not be properly decoded
+    /// into an `i64`.
+    RateLimitI64,
+    /// When the decoding of a ratelimit header could not be properly decoded
+    /// from UTF-8.
+    RateLimitUtf8,
+    /// When a status is received, but the verification to ensure the response
+    /// is valid does not recognize the status.
+    UnknownStatus(u16),
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut Formatter) -> FmtResult {
+        f.write_str(self.description())
+    }
+}
+
+impl StdError for Error {
+    fn description(&self) -> &str {
+        match *self {
+            Error::InvalidRequest(_) => "Received an unexpected status code",
+            Error::RateLimitI64 => "Error decoding a header into an i64",
+            Error::RateLimitUtf8 => "Error decoding a header from UTF-8",
+            Error::UnknownStatus(_) => "Verification does not understand status",
+        }
+    }
+}