Merge #262

262: Merge asm implementations r=therealprof a=jonas-schievink

This replaces the implementation of `inline-asm` with the file I wrote in #259 (and some fixes).

All functions that call assembly now do so via a `call_asm!` macro that either dispatches to a call to an `#[inline(always)]` function containing the inline `asm!`, or to the FFI shim. This makes all functions that call into asm significantly shorter.

The FFI shim is now also macro-generated, which makes it very small.

Co-authored-by: Jonas Schievink <jonasschievink@gmail.com>

Author: bors[bot]

Diff for: .travis.yml

@@ -7,7 +7,7 @@ branches:
     - trying
 
 rust:
-  - 1.35.0
+  - 1.38.0
   - stable
   - nightly
 

Diff for: README.md

@@ -11,7 +11,7 @@ This project is developed and maintained by the [Cortex-M team][team].
 
 ## Minimum Supported Rust Version (MSRV)
 
-This crate is guaranteed to compile on stable Rust 1.31 and up. It might compile with older versions but that may change in any new patch release.
+This crate is guaranteed to compile on stable Rust 1.38 and up. It might compile with older versions but that may change in any new patch release.
 
 ## License