Improve some comments (#8)

* Less complicated are_primes_below example

* Spelling

* Remove mention of isqrt

src/lib.rs

@@ -72,8 +72,8 @@
 #![cfg_attr(not(test), no_std)]
 
 /// The functions that return or take integers use this type. Currently `u32`.
-// Just change this to whatever unsigned primitive integer type you want and it should work as long as it has enough bits for your purposes (and you change the special case in isqrt).
-// This is used since there is currenlty no way to be generic over types that can do arithmetic at compile time.
+// Just change this to whatever unsigned primitive integer type you want and it should work as long as it has enough bits for your purposes.
+// This is used since there is currently no way to be generic over types that can do arithmetic at compile time.
 type Underlying = u32;
 
 mod imath;