Allow experimental slicing syntax

* Enables the feature-gate for slicing
* Removes `use std::slice::Slice` since it is included in the prelude.
Merge pull request #188 from drbawb/feature/fix-slices

Keep slicing syntax compiling after nightly update
Allow experimental slicing syntax

* Enables the feature-gate for slicing
* Removes `use std::slice::Slice` since it is included in the prelude.
sdl2::render::lock now returns the pitch as well
cleaner and safer code
renaming lock() to with_lock()
lock_with -> with_lock, priv unlock
changes for latest rust, change static to const
Merge pull request #190 from bbodi/static

changes to latest rust - changing static to const
Merge pull request #189 from bbodi/lock

Safer and more consistent Texture.lock funtion
Updated SDL version used in the travis build.
Merge pull request #196 from stykr/master

Updated SDL version used in the travis build = passes
Added `#[repr(C)]`

According to the FFI guide, structs are only guaranteed to be
compatible when annotated with `#[repr(C)]`.
Fixed mouse wheel bug

Closes https://github.com/AngryLawyer/rust-sdl2/issues/197
Merge pull request #198 from bvssvni/master

Added `#[repr(C)]`
changes for removal of libdebug in latest

* replace {:?}
* remove debug crate
get_ticks returns u32 instead of uint
Merge pull request #200 from bbodi/tick_ui32

get_ticks returns u32 instead of uint
Merge pull request #199 from jdeseno/latest-rust

changes for removal of libdebug in latest