Merge #442: Explicitly do not support 16 bit architectures

d02c313 Explicitly do not support 16 bit architectures (Tobin C. Harding)

Pull request description:

  We cast `u32` to `usize` in a bunch of places, this will cause strange behaviour because of truncation on 16 bit architectures.

  Add a compile time check to explicitly not support 16 bit architectures.

ACKs for top commit:
  apoelstra:
    ACK d02c313

Tree-SHA512: 11466e173913c5337f9a4ea03a4df5ee6be809ca32987494881d470c87a41f9cca77dde7ed68289896cce5cc875b89ab34a164ea2f4dc41b9fbe6e0ab9a62e71

Author: sanket1729

src/lib.rs

@@ -90,6 +90,11 @@
 #![deny(unused_imports)]
 #![deny(missing_docs)]
 
+#[cfg(target_pointer_width = "16")]
+compile_error!(
+    "rust-miniscript currently only supports architectures with pointers wider than 16 bits"
+);
+
 pub use bitcoin;
 
 #[cfg(not(feature = "std"))]