Fix some documentation typos

src/doc/reference.md

@@ -2368,7 +2368,7 @@ The currently implemented features of the reference compiler are:
                     removed entirely for something more wholesome.
 
 * `custom_attribute` - Allows the usage of attributes unknown to the compiler
-                       so that new attributes can be added in a bacwards compatible
+                       so that new attributes can be added in a backwards compatible
                        manner (RFC 572).
 
 * `custom_derive` - Allows the use of `#[derive(Foo,Bar)]` as sugar for
@@ -2397,7 +2397,7 @@ The currently implemented features of the reference compiler are:
                  nasty hack that will certainly be removed.
 
 * `main` - Allows use of the `#[main]` attribute, which changes the entry point
-           into a Rust program. This capabiilty is subject to change.
+           into a Rust program. This capability is subject to change.
 
 * `macro_reexport` - Allows macros to be re-exported from one crate after being imported
                      from another. This feature was originally designed with the sole
@@ -2453,7 +2453,7 @@ The currently implemented features of the reference compiler are:
                     is unintuitive and suboptimal.
 
 * `start` - Allows use of the `#[start]` attribute, which changes the entry point
-            into a Rust program. This capabiilty, especially the signature for the
+            into a Rust program. This capability, especially the signature for the
             annotated function, is subject to change.
 
 * `struct_inherit` - Allows using struct inheritance, which is barely

src/libsyntax/feature_gate.rs

@@ -10,7 +10,7 @@
 
 //! Feature gating
 //!
-//! This modules implements the gating necessary for preventing certain compiler
+//! This module implements the gating necessary for preventing certain compiler
 //! features from being used by default. This module will crawl a pre-expanded
 //! AST to ensure that there are no features which are used that are not
 //! enabled.