Use correct macro for fetching zval string length (#33)

Author: jmikola

Book/hashtables/hashtable_api.rst

@@ -187,8 +187,8 @@ The only caveat is what "string length" means in this context: In the hashtable
 which do not include the NUL byte in the string length.
 
 What does this mean practically? When passing a literal string, the string length will be ``sizeof("foo")`` rather than
-``sizeof("foo")-1``. When passing a string from a zval, the string length will be ``Z_STRVAL_P(zv)+1`` rather than
-``Z_STRVAL_P(zv)``.
+``sizeof("foo")-1``. When passing a string from a zval, the string length will be ``Z_STRLEN_P(zv)+1`` rather than
+``Z_STRLEN_P(zv)``.
 
 Apart from this the functions are used in exactly the same way as the index functions::
 
@@ -742,4 +742,4 @@ The last of the comparison-related function is used for finding the smallest or
     );
 
 For ``flag=0`` the minimum value is written into ``pData``, for ``flag=1`` the maximum value. If the hashtable is empty
-the function will return ``FAILURE`` (as min/max are not well-defined for an empty array).
+the function will return ``FAILURE`` (as min/max are not well-defined for an empty array).