Spelling fixes and link addition about LRU cache in the docs.

ethcore/light/src/cache.rs

@@ -61,6 +61,7 @@ impl Default for CacheSizes {
 ///
 /// Note that almost all getter methods take `&mut self` due to the necessity to update
 /// the underlying LRU-caches on read.
+/// [LRU-cache](https://en.wikipedia.org/wiki/Cache_replacement_policies#Least_Recently_Used_.28LRU.29)
 pub struct Cache {
 	headers: MemoryLruCache<H256, encoded::Header>,
 	canon_hashes: MemoryLruCache<BlockNumber, H256>,

ethcore/light/src/cht.rs

@@ -15,7 +15,7 @@
 //!
 //! Each CHT is a trie mapping block numbers to canonical hashes and total difficulty.
 //! One is generated for every `SIZE` blocks, allowing us to discard those blocks in
-//! favor the the trie root. When the "ancient" blocks need to be accessed, we simply
+//! favor of the trie root. When the "ancient" blocks need to be accessed, we simply
 //! request an inclusion proof of a specific block number against the trie with the
 //! root has. A correct proof implies that the claimed block is identical to the one
 //! we discarded.

ethcore/light/src/net/mod.rs

@@ -14,7 +14,7 @@
 // You should have received a copy of the GNU General Public License
 // along with Parity.  If not, see <http://www.gnu.org/licenses/>.
 
-//! PIP Protocol Version 1 implementation.
+//! PLP Protocol Version 1 implementation.
 //!
 //! This uses a "Provider" to answer requests.