use sphinx instead of mkdocs

mkdocs.yml

@@ -1,16 +0,0 @@
-site_name: Lark
-theme: readthedocs
-pages:
-    - Main Page: index.md
-    - Philosophy: philosophy.md
-    - Features: features.md
-    - Parsers: parsers.md
-    - How To Use (Guide): how_to_use.md
-    - How To Develop (Guide): how_to_develop.md
-    - Grammar Reference: grammar.md
-    - Tree Construction Reference: tree_construction.md
-    - Visitors and Transformers: visitors.md
-    - Classes Reference: classes.md
-    - Recipes: recipes.md
-    - Import grammars from Nearley: nearley.md
-    - Tutorial - JSON Parser: json_tutorial.md

readthedocs.yml

@@ -1,10 +1,7 @@
 version: 2
 
-mkdocs:
-  configuration: mkdocs.yml
-  fail_on_warning: false
-
 formats: all
 
-python:
-  version: 3.5
+# Build documentation in the docs/ directory with Sphinx
+sphinx:
+  configuration: docs/conf.py