Combo converter doc (#735)

docs/dynamic.md

@@ -44,6 +44,20 @@ from dynaconf import settings
 settings.DB_PATH == '~/DEVELOPMENT/calculator/mydb.db'
 ```
 
+`@format` token can be used together with tokens like `@str`, `@int`, `@float`, `@bool`, and `@json` to cast the results parsed by `@format`.
+
+Example: 
+
+Casting to integer from `@format` templated values
+
+```yaml
+NUM_GPUS: 4
+# This returns the integer after parsing
+FOO_INT: "@int @format {this.NUM_GPUS}"
+# This returns the string after parsing
+FOO_STR: "@format {this.NUM_GPUS}"
+```
+
 ### @jinja token
 
 If `jinja2` package is installed then dynaconf will also allow the use jinja to render string values.
@@ -75,3 +89,44 @@ settings.DB_PATH == '~/development/calculator/mydb.db'
 The main difference is that Jinja allows some Python expressions to be evaluated such as `{% for, if, while %}` and also supports calling methods and has lots of filters like `| lower`.
 
 Jinja supports its built-in filters listed in [Builtin Filters Page](http://jinja.palletsprojects.com/en/master/templates/#builtin-filters) and Dynaconf includes additional filters for `os.path` module: `abspath`. `realpath`, `relpath`, `basename` and `dirname` and usage is like: `VALUE = "@jinja {{this.FOO | abspath}}"`
+
+`@jinja` token can be used together with tokens like `@str`, `@int`, `@float`, `@bool`, and `@json` to cast the results parsed by `@jinja`.
+
+Example:
+
+Casting to integer from `@jinja` templated values
+
+```yaml
+NUM_GPUS: 4
+# This returns the integer after parsing
+FOO_INT: "@int @jinja {{ this.NUM_GPUS }}"
+# This returns the string after parsing
+FOO_STR: "@jinja {{ this.NUM_GPUS }}"
+```
+
+Example:
+
+Casting to a `json` dict from `@jinja` templated values
+
+```yaml
+MODEL_1:
+  MODEL_PATH: "src.main.models.CNNModel"
+  GPU_COUNT: 4
+  OPTIMIZER_KWARGS:
+    learning_rate: 0.002
+
+MODEL_2:
+  MODEL_PATH: "src.main.models.VGGModel"
+  GPU_COUNT: 2
+  OPTIMIZER_KWARGS:
+    learning_rate: 0.001
+
+# Flag to choose which model to use
+MODEL_TYPE: "MODEL_2"
+
+# This returns the dict loaded from the resulting json
+MODEL_SETTINGS_DICT: "@json @jinja {{ this|attr(this.MODEL_TYPE) }}"
+
+# This returns the raw json string
+MODEL_SETTINGS_STR: "@jinja {{ this|attr(this.MODEL_TYPE) }}"
+```