New docs are in mkdocs (#4178)

* start mkdocs

* simple docs for tensor

* more docs

* move those back

* more docs

* copy markdown extensions

* docs legacy

* docs building workflow

* fix showcase links

* only that?

* install tinygrad

* add docs to setup.py

* Delete examples/llm.c/data

docs/nn.md

@@ -0,0 +1,17 @@
+## Neural Network classes
+
+::: tinygrad.nn
+    options:
+        members: true
+
+## Optimizers
+
+::: tinygrad.nn.optim
+    options:
+        members: true
+
+## Load/Save
+
+::: tinygrad.nn.state
+    options:
+        members: true