build: make alloc a normal dependency

The `alloc` feature was stabilized with rustc-1.36, so drop the
unstable tag and make it a core dependency.

Signed-off-by: David Rheinsberg <david.rheinsberg@gmail.com>

Author: dvdhrm

README.md

@@ -19,7 +19,7 @@ ISO-8859-1 based string.
 
 The requirements for this project are:
 
- * `rustc >= 1.31.0`
+ * `rustc >= 1.36.0`
 
 ### Build
 

src/lib.rs

@@ -10,12 +10,9 @@
 
 // We currently need some unstable features:
 //
-//  * We import `liballoc` since we want to explicitly allow running in no-std environments with
-//    custom allocators.
-//
 //  * We use `doc_cfg` to run conditional code in rustdoc compilations. This is, again, related to
 //    `no_std`, since we want to make sure the rustdoc examples still work correctly.
-#![feature(alloc, doc_cfg)]
+#![feature(doc_cfg)]
 
 // We do not depend on `libstd`, but pull it in for our unit tests and documentation.
 #![cfg_attr(not(any(test, rustdoc)), no_std)]