[IMP] owl: introduce dev mode

This commit adds a static key 'dev' on QWeb (which acts as a central
point of access in owl internal code), and a 'mode' key on the value
exported by owl to let external code manipulate it.

closes #117

doc/readme.md

@@ -13,4 +13,5 @@
 ## Miscellaneous
 - [Quick Start](quick_start.md)
 - [Animations](animations.md)
+- [Tooling](tooling.md)
 - [Comparison with React/Vue](comparison.md)

doc/tooling.md

@@ -0,0 +1,18 @@
+# 🦉 Tooling 🦉
+
+## Development mode
+
+By default, Owl is in *production* mode, this means that it will try to do its
+job fast, and skip some expensive operations.  However, in some cases, it is
+convenient to have better information on what is going on, this is the purpose
+of the dev mode.
+
+Owl has a mode flag, in `owl.__info__.mode`.  Its default value is `prod`, but
+it can be set to `dev`:
+
+```js
+owl.__info__.mode = 'dev';
+```
+
+Note that templates compiled with the `prod` settings will not be recompiled.
+So, changing this setting is best done at startup.