Added docs, integer fields and refactored models.TextField to use CharField

I realized that per the django forms, there is no need for a separate
TextField, an unlimited CharField is perfectly good.
Also added default field for the different IntegerField types

docs/api-guide/fields.md

@@ -73,18 +73,35 @@ These fields represent basic datatypes, and support both reading and writing val
 
 ## BooleanField
 
+A Boolean representation, corresponds to `django.db.models.fields.BooleanField`.
+
 ## CharField
 
+A text representation, optionally validates the text to be shorter than `max_length` and longer than `min_length`, corresponds to `django.db.models.fields.CharField`
+or `django.db.models.fields.TextField`.
+
+**Signature:** `CharField([max_length=<Integer>[, min_length=<Integer>]])`
+
 ## EmailField
 
+A text representation, validates the text to be a valid e-mail adress. Corresponds to `django.db.models.fields.EmailField`
+
 ## DateField
 
+A date representation. Corresponds to `django.db.models.fields.DateField`
+
 ## DateTimeField
 
+A date and time representation. Corresponds to `django.db.models.fields.DateTimeField`
+
 ## IntegerField
 
+An integer representation. Corresponds to `django.db.models.fields.IntegerField`, `django.db.models.fields.SmallIntegerField`, `django.db.models.fields.PositiveIntegerField` and `django.db.models.fields.PositiveSmallIntegerField`
+
 ## FloatField
 
+A floating point representation. Corresponds to `django.db.models.fields.FloatField`.
+
 ---
 
 # Relational Fields

rest_framework/serializers.py

@@ -377,11 +377,14 @@ class ModelSerializer(Serializer):
         field_mapping = {
             models.FloatField: FloatField,
             models.IntegerField: IntegerField,
+            models.PositiveIntegerField: IntegerField,
+            models.SmallIntegerField: IntegerField,
+            models.PositiveSmallIntegerField: IntegerField,
             models.DateTimeField: DateTimeField,
             models.DateField: DateField,
             models.EmailField: EmailField,
             models.CharField: CharField,
-            models.TextField: TextField,
+            models.TextField: CharField,
             models.CommaSeparatedIntegerField: CharField,
             models.BooleanField: BooleanField,
         }