s//rust when relevant

It looks better on the wiki/the new documentation page.

Author: mcarton

CONTRIBUTING.md

@@ -41,7 +41,7 @@ contains some questionable code itself! Also before making a pull request, pleas
 travis build actually checks for this.
 
 Also please document your lint with a doc comment akin to the following:
-```
+```rust
 /// **What it does:** Describe what the lint matches.
 ///
 /// **Why is this bad?** Write the reason for linting the code.

clippy_lints/src/collapsible_if.rs

@@ -2,7 +2,7 @@
 //!
 //! For example, the lint would catch:
 //!
-//! ```
+//! ```rust
 //! if x {
 //!     if y {
 //!         println!("Hello world");

clippy_lints/src/entry.rs

@@ -11,7 +11,7 @@ use utils::{get_item_name, match_type, paths, snippet, span_lint_and_then, walk_
 /// **Why is this bad?** Using `entry` is more efficient.
 ///
 /// **Known problems:** Some false negatives, eg.:
-/// ```
+/// ```rust
 /// let k = &key;
 /// if !m.contains_key(k) { m.insert(k.clone(), v); }
 /// ```

clippy_lints/src/format.rs

@@ -65,7 +65,7 @@ impl LateLintPass for Pass {
 }
 
 /// Checks if the expressions matches
-/// ```
+/// ```rust
 /// { static __STATIC_FMTSTR: &[""] = _; __STATIC_FMTSTR }
 /// ```
 fn check_static_str(cx: &LateContext, expr: &Expr) -> bool {
@@ -91,7 +91,7 @@ fn check_static_str(cx: &LateContext, expr: &Expr) -> bool {
 }
 
 /// Checks if the expressions matches
-/// ```
+/// ```rust
 /// &match (&42,) {
 ///     (__arg0,) => [::std::fmt::ArgumentV1::new(__arg0, ::std::fmt::Display::fmt)],
 /// })

clippy_lints/src/misc.rs

@@ -357,7 +357,7 @@ impl LateLintPass for ModuloOne {
 /// **Known problems:** None
 ///
 /// **Example**:
-/// ```
+/// ```rust
 /// match v {
 ///     Some(x) => (),
 ///     y @ _   => (), // easier written as `y`,
@@ -399,7 +399,7 @@ impl LateLintPass for PatternPass {
 /// allowed in the mean time.
 ///
 /// **Example**:
-/// ```
+/// ```rust
 /// let _x = 0;
 /// let y = _x + 1; // Here we are using `_x`, even though it has a leading underscore.
 ///                 // We should rename `_x` to `x`