some grammar corrections

Author: pvdrz

src/libcore/cell.rs

@@ -13,18 +13,19 @@
 //! Rust memory safety is based on this rule: Given an object `T`, it is only possible to
 //! have one of the following:
 //!
-//! - Having several immutable references (`&T`) to the object (also know as Aliasing).
-//! - Having one mutable reference (`&mut T`) to the object (also know as Mutability).
+//! - Having several immutable references (`&T`) to the object (also known as **aliasing**).
+//! - Having one mutable reference (`&mut T`) to the object (also known as **mutability**).
 //!
 //! This is enforced by the Rust compiler. However, there are situations where this rule is not
 //! flexible enough. Sometimes it is required to have multiple references to an object and yet
 //! mutate it.
 //!
-//! Shareable mutable containers exist to permit mutability in the presence of aliasing in a
-//! controlled manner. Both `Cell<T>` and `RefCell<T>` allows to do this in a single threaded
+//! Shareable mutable containers exist to permit mutability in a controlled manner, even in the
+//! presence of aliasing. Both `Cell<T>` and `RefCell<T>` allows to do this in a single threaded
 //! way. However, neither `Cell<T>` nor `RefCell<T>` are thread safe (they do not implement
-//! `Sync`), if you need to do Aliasing and Mutation between multiple threads is possible to use
-//! [`Mutex`](../../std/sync/struct.Mutex.html), [`RwLock`](../../std/sync/struct.RwLock.html) or
+//! `Sync`). If you need to do aliasing and mutation between multiple threads it is possible to
+//! use [`Mutex`](../../std/sync/struct.Mutex.html),
+//! [`RwLock`](../../std/sync/struct.RwLock.html) or
 //! [`atomic`](../../core/sync/atomic/index.html) types.
 //!
 //! Values of the `Cell<T>` and `RefCell<T>` types may be mutated through shared references (i.e.