Add inline to some small functions used in sse impl

This speeds up the criteron benchmarks by almost 2x

I believe this is needed because e.g. Bytes::find is inlined, and calls `find`
generically, which will call PackedCompareControl methods. So the code calling
the methods will be inlined into the calling crate, but the implemetations of
the PackedCompareControl are not accessable to the code in the calling crate,
so they will end up as actual function calls. However these functions are
_super_ simple, and inlining them helps a LOT, so adding `#[inline]` to these
functions, and making their implementation available to calling crates has a
huge effect.

This was only seen when moving to criterion because previously, nightly
benchmarks were implemented in the library crate itself, and so these functions
were already elegable for inlining. Criteron results were actually more
accurate to what callers of the crate would actually see!

src/simd.rs

@@ -252,9 +252,12 @@ impl Bytes {
 }
 
 impl<'b> PackedCompareControl for &'b Bytes {
+    #[inline]
     fn needle(&self) -> __m128i {
         self.needle
     }
+
+    #[inline]
     fn needle_len(&self) -> i32 {
         self.needle_len
     }
@@ -312,9 +315,12 @@ impl<'a> ByteSubstring<'a> {
 }
 
 impl<'a, 'b> PackedCompareControl for &'b ByteSubstring<'a> {
+    #[inline]
     fn needle(&self) -> __m128i {
         self.needle
     }
+
+    #[inline]
     fn needle_len(&self) -> i32 {
         self.needle_len
     }