Make this crate no_std

As nothing actually depends on std, there is no need to keep a
dependency on it.  This allows users such as the jid crate to actually
be no_std as well.

Author: linkmauve

src/lib.rs

@@ -1,13 +1,16 @@
 //! An implementation of the "stringprep" algorithm defined in [RFC 3454][].
 //!
 //! [RFC 3454]: https://tools.ietf.org/html/rfc3454
+#![no_std]
 #![warn(missing_docs)]
+extern crate alloc;
 extern crate unicode_bidi;
 extern crate unicode_normalization;
 extern crate unicode_properties;
 
-use std::borrow::Cow;
-use std::fmt;
+use alloc::borrow::Cow;
+use alloc::string::String;
+use core::fmt;
 use unicode_normalization::UnicodeNormalization;
 use unicode_properties::{GeneralCategoryGroup, UnicodeGeneralCategory};
 
@@ -44,7 +47,7 @@ impl fmt::Display for Error {
     }
 }
 
-impl std::error::Error for Error {}
+impl core::error::Error for Error {}
 
 /// Prepares a string with the SASLprep profile of the stringprep algorithm.
 ///

src/tables.rs

@@ -1,6 +1,6 @@
 //! Character Tables
-use std::cmp::Ordering;
-use std::str::Chars;
+use core::cmp::Ordering;
+use core::str::Chars;
 use unicode_bidi::{bidi_class, BidiClass};
 use unicode_properties::{GeneralCategoryGroup, UnicodeGeneralCategory};