doc: Refactors the documentation

This commit refactors the documentation according to my proposal in #1273
and the discussion I had with fd0 on IRC.

The bits from the manual that I could not immediately put into the new
structure are contained in manual_rest.rst Anything else is still there,
nothing has been deleted.

I changed the heading markup to follow the convention used in Python’s
Style Guide for documentation, this convention is explained in a comment
at the top of every file.

I also added a paragraph on installing restic on Debian.

doc/050_restore.rst

@@ -0,0 +1,73 @@
+..
+  Normally, there are no heading levels assigned to certain characters as the structure is
+  determined from the succession of headings. However, this convention is used in Python’s
+  Style Guide for documenting which you may follow:
+
+  # with overline, for parts
+  * for chapters
+  = for sections
+  - for subsections
+  ^ for subsubsections
+  " for paragraphs
+
+#####################
+Restoring from backup
+#####################
+
+Restoring from a snapshot
+=========================
+
+Restoring a snapshot is as easy as it sounds, just use the following
+command to restore the contents of the latest snapshot to
+``/tmp/restore-work``:
+
+.. code-block:: console
+
+    $ restic -r /tmp/backup restore 79766175 --target /tmp/restore-work
+    enter password for repository:
+    restoring <Snapshot of [/home/user/work] at 2015-05-08 21:40:19.884408621 +0200 CEST> to /tmp/restore-work
+
+Use the word ``latest`` to restore the last backup. You can also combine
+``latest`` with the ``--host`` and ``--path`` filters to choose the last
+backup for a specific host, path or both.
+
+.. code-block:: console
+
+    $ restic -r /tmp/backup restore latest --target /tmp/restore-art --path "/home/art" --host luigi
+    enter password for repository:
+    restoring <Snapshot of [/home/art] at 2015-05-08 21:45:17.884408621 +0200 CEST> to /tmp/restore-art
+
+Use ``--exclude`` and ``--include`` to restrict the restore to a subset of
+files in the snapshot. For example, to restore a single file:
+
+.. code-block:: console
+
+    $ restic -r /tmp/backup restore 79766175 --target /tmp/restore-work --include /work/foo
+    enter password for repository:
+    restoring <Snapshot of [/home/user/work] at 2015-05-08 21:40:19.884408621 +0200 CEST> to /tmp/restore-work
+
+This will restore the file ``foo`` to ``/tmp/restore-work/work/foo``.
+
+Restore using mount
+===================
+
+Browsing your backup as a regular file system is also very easy. First,
+create a mount point such as ``/mnt/restic`` and then use the following
+command to serve the repository with FUSE:
+
+.. code-block:: console
+
+    $ mkdir /mnt/restic
+    $ restic -r /tmp/backup mount /mnt/restic
+    enter password for repository:
+    Now serving /tmp/backup at /mnt/restic
+    Don't forget to umount after quitting!
+
+Mounting repositories via FUSE is not possible on Windows and OpenBSD.
+
+Restic supports storage and preservation of hard links. However, since
+hard links exist in the scope of a filesystem by definition, restoring
+hard links from a fuse mount should be done by a program that preserves
+hard links. A program that does so is ``rsync``, used with the option
+--hard-links.
+