Merge pull request #33 from ijackson/doc-para

Break a long docs para

src/instant.rs

@@ -9,8 +9,9 @@ use super::duration::*;
 #[allow(unused_imports)]
 use super::helpers::*;
 
-/// A measurement of a *monotonically* increasing clock. Opaque and useful only
-/// with `Duration`.
+/// A measurement of a *monotonically* increasing clock.
+///
+/// Opaque and useful only with `Duration`.
 /// Resulting durations are actual durations; they do not get affected by
 /// clock adjustments, leap seconds, or similar.
 /// In order to get a measurement of the *wall clock*, use `Date` instead.