Added from_stride function to compose stride iterators
Handles case where from_stride step does not divide the number of elements evenly
Merge branch 'master' into mutable_stride

Conflicts:
	src/stride.rs
Added mutable strides
Cargo.toml: disable doctests for lib.rs
Rename to StrideMut, and rename some methods

See upcoming new conventions for rust with suffixed mut for methods (and
presumably types).
stride: Fix from_stride to not use .offset on NULL

Apart from feeling cleaner, this is UB in llvm, so we must avoid it.
stride: Small simplification in iterator macro