Add Features for Easy Web App Creation

[kyleingraham]

Restructure Potcake for easy web app creation. Web apps can be created through two new objects. WebApp and WebAppSettings. Through them we provide the following features:

• Django-style routing
• Static file serving (with collection of files from multiple directories)
• Django-style URL reversing
• Middleware
• Settings management

Details:

Revamp URL dispatching to provide an ergonomic API free of templates. Path parsing is now done at runtime which frees us from the struggles templates bring. Templates are great but use of them for central data structures forces user code to be templated. It also makes some API structures impossible to right. For example, with templates the user cannot store configuration as data prior to instantiating the WebApp if the configuration uses templates that need the WebApp. Also, each instantiation is a new type if the template arguments differ. This prevents storing template instantiations in a collection. We make heavy use of delegates for storing code to use an object instead of objects themselves. This is handy for storing disparate objects in a collection when they all are alike in the actions carried out using them.

Add the ability to obtain a route path by supplying a pre-registered name and path arguments (reversing). The reversing function makes use of a new reference to the initialize app at runtime.

Add toPath functions to path converters for converting path arguments to their string representations in paths. Return a common exception from path converters to aid signaling when a reversed path cannot be created. Use Variant instead of emplacing and cast for easier-to-use code.

Rehash Router associative arrays for performance.

Add static file handling via two approaches:

• Single-directory approach where all files are stored in a single directory in
  development and production.
• Collecting approach where static files are merged into one directory and served from a single routh path.

Add staticPath method for building static paths in templates.

Add WebApp.addRoutes for adding all routes at once using a collection. Make a trailing '/' optional when calling a route if the route's path was specified with a trailing '/'

Streamline static file serving for the single directory case. The developer can configure serving via the settings object and all static serving for all cases is now done via serveStaticFiles.

Wrap all modules in @safe.