Don't use a `StdResult` alias for better docs.

This is a pretty opinionated change, but I find documentation to be
clearer when using plain old names everybody understands immediately.

src/error.rs

@@ -1,6 +1,5 @@
 use std::fmt;
 use std::sync::Arc;
-use std::result::Result as StdResult;
 
 use failure;
 
@@ -112,7 +111,7 @@ pub enum Error {
 }
 
 /// A specialized `Result` type used by `rlua`'s API.
-pub type Result<T> = StdResult<T, Error>;
+pub type Result<T> = ::std::result::Result<T, Error>;
 
 impl fmt::Display for Error {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
@@ -203,7 +202,7 @@ pub trait ExternalResult<T> {
     fn to_lua_err(self) -> Result<T>;
 }
 
-impl<T, E> ExternalResult<T> for StdResult<T, E>
+impl<T, E> ExternalResult<T> for ::std::result::Result<T, E>
 where
     E: ExternalError,
 {