Cache the default rendered home page

A bit hacky, since CLForm can't seem to initialize properly without
being part of a request. To avoid a reference-before-assignment error,
the INDEX variable is first initialized as a global in __init__.py. But
it is definitely faster. Repeated renders take around 2ms each. Reading
the cached value takes about 0.002ms.

Also split index() into index_get() and index_post(), since GET calls
always use the cached version, and POST calls never do.

flaskr/__init__.py

@@ -10,6 +10,8 @@ from flask import (
 
 import writing
 
+INDEX = None
+
 def optimize_css():
     import re
     root = os.path.dirname(os.getcwd())

writing.py

@@ -5,6 +5,7 @@ from wtforms import Form, BooleanField, StringField, TextAreaField, validators
 import urllib.parse
 
 from latty import CLData
+import flaskr
 
 
 writing_blueprint = Blueprint('writing', __name__,)
@@ -47,10 +48,19 @@ class CLForm(Form):
         default=body_string
     )
 
-@writing_blueprint.route('/', methods=('GET', 'POST'))
-def index():
+@writing_blueprint.route('/', methods=['GET'])
+def index_get():
+    if flaskr.INDEX == None:
+        flaskr.INDEX = render_template(
+            'writing.html',
+            form=CLForm()
+        )
+    return flaskr.INDEX
+
+@writing_blueprint.route('/', methods=['POST'])
+def index_post():
     form = CLForm(request.form)
-    if request.method == 'POST' and form.validate():
+    if form.validate():
         data = CLData(
             username=form.username.data,
             company=form.company.data,