docs: Fix typos.

Used codespell and manual fixes.

Refs: #4442

docs/contributing.rst

@@ -110,13 +110,13 @@ Example: ``./test/libsolidity/syntaxTests/double_stateVariable_declaration.sol``
     // ----
     // DeclarationError: Identifier already declared.
 
-A syntax test must contain at least the contract under test itself, followed by the seperator ``----``. The additional comments above are used to describe the
+A syntax test must contain at least the contract under test itself, followed by the separator ``----``. The additional comments above are used to describe the
 expected compiler errors or warnings. This section can be empty in case that the contract should compile without any errors or warnings.
 
 In the above example, the state variable ``variable`` was declared twice, which is not allowed. This will result in a ``DeclarationError`` stating that the identifier was already declared.
 
 The tool that is being used for those tests is called ``isoltest`` and can be found under ``./test/tools/``. It is an interactive tool which allows
-editing of failing contracts using your prefered text editor. Let's try to break this test by removing the second declaration of ``variable``:
+editing of failing contracts using your preferred text editor. Let's try to break this test by removing the second declaration of ``variable``:
 
 ::
 
@@ -237,7 +237,7 @@ Othwerise, upon execution the fuzzer will halt with an error saying binary is no
              Location : check_binary(), afl-fuzz.c:6920
 
 
-Next, you need some example source files. This will make it much easer for the fuzzer
+Next, you need some example source files. This will make it much easier for the fuzzer
 to find errors. You can either copy some files from the syntax tests or extract test files
 from the documentation or the other tests: