Mainly fixed the code to make it work again, and cleaned a lot.

Documentation updates:

- updated the installation procedure
- removed some backlog items (from the roadmap too) and put them as GitHub issues
- removed parts of the documentation obsolete due to the fixes described below
- cleaned and fixed the documentation in general

Updating:

- fixed the communication with the backend, to use proper modules and methods, with the right workflow
- commented broken code

Cleaning:

- removed old unecessary code
- changed big blocks of comments (for visual emphasis): replaced the repeated slashes by stars instead
- changed constant naming scheme (for RPC): now the type of the contant (key, member name, etc.) is put before, for better visual recognition when they are grouped
- fixed some little formatting quirks
- replaced some unchecked casts with safe casts

Backend:

- fixed handling of exceptions from the backend: the exceptions were received form the backend as normal objects, so the Backend class believed there were never error. Now the response status is checked.
- added a custom exception class for backend's exceptions
- added convenient methods to use the backend's editor module and more specifically execute mode's services
- refactred the code for more granularity, maintainability, etc.

Document:

- fixed the model of a document, now it contains only one attribute, which is the document ID returned by the backend

Outline:

- fixed it: wrong key was used to access root access
- more safety on content providing

Activator:

- the plugin doesn't fail at startup anymore if no backend can be found nor launched (however it might still fail at the Editor component level)

Folding:

- fixed it: it simply uses the latest backend options to get the data it actually uses

Updated the main documentation file.

Closes #8
v0.0.1
Implementation of the validation method.
Outline and folding have also been inhibited.

Manifest
- change of some bundles versions

Plugin
- Extension for a custom marker for aria templates errors

Document
- implementation of methods to add, remove, and format the error message of markers. Markers are added directly on the file.

Document listener
- removal of error markers after a document change

Marker Annotation Hover
- implmentation of a class that is in charge of creating the message to diplay when the user hovers on a marker.
Source update on save

The purpose of this commit is to avoid the update of the source every time the content of a document changes. Since we intend to perform parsing and validation only on save, it doesn't make sense to have an update of the source more often.

Backend
- arguments for service function have a more generic type

Document
- addition of a list of changes that are notified by Document Listener
- method to call the backend service to update the source

Document Listener
- removal of the update service, changes are just notified to the document
- call to the updateSource method of the document when the document is saved