Added support for multiple API versions

Note that no changes were made to the api, the code was refactored to allow for new versions of the api to be created down the road.

Here's what this would look like:
+-- api/
    +-- v1/
        +-- __init__.py
        +-- resources.py
    +-- v1_1/
        +-- __init__.py
        +-- resources.py
    +-- v2/
        +-- __init__.py
        +-- resources.py
    +-- __init__.py
    +-- common.py

ihatemoney/api/common.py

@@ -1,7 +1,6 @@
 # coding: utf8
-from flask import Blueprint, request, current_app
+from flask import request, current_app
-from flask_restful import Resource, Api, abort
+from flask_restful import Resource, abort
-from flask_cors import CORS
 from wtforms.fields.core import BooleanField
 
 from ihatemoney.models import db, Project, Person, Bill
@@ -9,12 +8,6 @@ from ihatemoney.forms import ProjectForm, EditProjectForm, MemberForm, get_billf
 from werkzeug.security import check_password_hash
 from functools import wraps
 
-
-api = Blueprint("api", __name__, url_prefix="/api")
-CORS(api)
-restful_api = Api(api)
-
-
 def need_auth(f):
     """Check the request for basic authentication for a given project.
 
@@ -196,18 +189,3 @@ class TokenHandler(Resource):
         token = project.generate_token()
         return {"token": token}, 200
     
-
-restful_api.add_resource(ProjectsHandler, "/projects")
-restful_api.add_resource(ProjectHandler, "/projects/<string:project_id>")
-restful_api.add_resource(TokenHandler, "/projects/<string:project_id>/token")
-restful_api.add_resource(MembersHandler, "/projects/<string:project_id>/members")
-restful_api.add_resource(
-    ProjectStatsHandler, "/projects/<string:project_id>/statistics"
-)
-restful_api.add_resource(
-    MemberHandler, "/projects/<string:project_id>/members/<int:member_id>"
-)
-restful_api.add_resource(BillsHandler, "/projects/<string:project_id>/bills")
-restful_api.add_resource(
-    BillHandler, "/projects/<string:project_id>/bills/<int:bill_id>"
-)

ihatemoney/api/v1/__init__.py

@@ -0,0 +1 @@
+from .resources import api

ihatemoney/api/v1/resources.py

@@ -0,0 +1,26 @@
+# coding: utf8
+from flask import Blueprint
+from flask_restful import Api
+from flask_cors import CORS
+
+from ihatemoney.api.common import ProjectsHandler, ProjectHandler, TokenHandler\
+    , MemberHandler, ProjectStatsHandler, MembersHandler, BillHandler, BillsHandler
+
+api = Blueprint("api", __name__, url_prefix="/api")
+CORS(api)
+restful_api = Api(api)
+
+restful_api.add_resource(ProjectsHandler, "/projects")
+restful_api.add_resource(ProjectHandler, "/projects/<string:project_id>")
+restful_api.add_resource(TokenHandler, "/projects/<string:project_id>/token")
+restful_api.add_resource(MembersHandler, "/projects/<string:project_id>/members")
+restful_api.add_resource(
+    ProjectStatsHandler, "/projects/<string:project_id>/statistics"
+)
+restful_api.add_resource(
+    MemberHandler, "/projects/<string:project_id>/members/<int:member_id>"
+)
+restful_api.add_resource(BillsHandler, "/projects/<string:project_id>/bills")
+restful_api.add_resource(
+    BillHandler, "/projects/<string:project_id>/bills/<int:bill_id>"
+)

ihatemoney/run.py

@@ -8,7 +8,7 @@ from flask_mail import Mail
 from flask_migrate import Migrate, upgrade, stamp
 from werkzeug.middleware.proxy_fix import ProxyFix
 
-from ihatemoney.api import api
+from ihatemoney.api.v1 import api as apiv1
 from ihatemoney.models import db
 from ihatemoney.utils import (
     IhmJSONEncoder,
@@ -132,7 +132,7 @@ def create_app(
 
     validate_configuration(app)
     app.register_blueprint(web_interface)
-    app.register_blueprint(api)
+    app.register_blueprint(apiv1)
     app.register_error_handler(404, page_not_found)
 
     # Configure the a, root="main"pplication