[account] Add warning when using is_valid_address (#13)

* [validator] Fix typo

* [account] Add thread warning to is_valid_address

pyhmy/account.py

@@ -28,6 +28,7 @@ _address_length = 42
 def is_valid_address(address) -> bool:
     """
     Check if given string is valid one address
+    NOTE: This function is NOT thread safe due to the C function used by the bech32 library.
 
     Parameters
     ----------

pyhmy/validator.py

@@ -32,7 +32,7 @@ _default_endpoint = 'http://localhost:9500'
 _default_timeout = 30
 
 
-# TODO: Add validator transcation functions
+# TODO: Add validator transaction functions
 # TODO: Add unit testing
 class Validator: