add new methods to the API docs (#326)

* add new methods to the API docs

docs/python_api.md

@@ -40,7 +40,10 @@ Here is a quick reference to some of the methods:
   recapitate
   annotate
   individuals_alive_at
+  individual_ages
   individual_ages_at
+  individual_parents
+  has_individual_parents
   slim_time
   convert_alleles
   generate_nucleotides
@@ -79,18 +82,36 @@ Additionally, ``pyslim`` contains the following methods:
 .. autofunction::  individuals_alive_at
 ```
 
+```{eval-rst}
+.. autofunction::  individual_ages
+```
+
 ```{eval-rst}
 .. autofunction::  individual_ages_at
 ```
 
 ```{eval-rst}
-.. autofunction::  slim_time
+.. autofunction::  individual_parents
+```
+
+```{eval-rst}
+.. autofunction::  has_individual_parents
 ```
 
 ```{eval-rst}
 .. autofunction::  population_size
 ```
 
+## Utilities
+
+```{eval-rst}
+.. autofunction::  slim_time
+```
+
+```{eval-rst}
+.. autofunction::  next_slim_mutation_id
+```
+
 
 ## Metadata