Password reset functionality

On the `reset` page an email address can be submitted. If an account
associated with the submitted email address an email is sent
containing an URL. This URL can be used to set a new password.

- Add GPLv3 for licensing
- Add dependencies
  - `rocket_contrib` to be able to use handlebar templates
  - `anyhow` to handle errors
  - `log` for logging
  - `ldap3` to communicate with a LDAP server
  - `lettre` and `lettre_email` to handle the generation of emails and
    to send them
  - `rand` to generate random keys
- Add `README.org` which is also used to generate `README.md`
- Add configuration parameters
  - domain
  - LDAP
    - server
    - base
    - filter
    - bind
    - password
- Change default development address to 0.0.0.0
- Add structs to handle data
- Add functions to handle password reset actions
  - `reset_prepare()` to generate a new key, send it to the requestor
    and keep it in the memory
  - `set_password()` to check for the key and set the password
- Add routes
- Add tests
- Add templates
  - `reset.html.hbs` to submit an email address
  - `reset_key.html.hbs` to set the new password

README.org

@@ -0,0 +1,43 @@
+* ldap0r
+  So far =ldap0r= is simply a very small web application just to reset
+  LDAP passwords. An user enters its email address, receives an email
+  containing a link to reset its LDAP password, thats it so far.
+
+** Installation
+   A rust nightly toolchain which can be aquired via https://rustup.rs
+   is needed in order to successfully build =ldap0r=. Install =rustup=,
+   download rust nightly, then clone this repository, set the
+   toolchain inside the source directory to nightly, build and run it.
+
+   #+BEGIN_SRC sh
+   rustup toolchain install nightly
+   git clone https://git.onders.org/finga/ldap0r.git
+   cd ldap0r
+   rustup override set nightly
+   cargo run
+   #+END_SRC
+
+   The application can be configured with the =Rocket.toml=
+   configuration file.
+
+** Todo List
+*** Password reset [5/10]
+**** DONE Form to send resetlink
+**** DONE Parse url with reset key
+**** DONE Cleanup all unwraps
+**** DONE Proper error handling
+**** DONE Implement proper logging
+**** TODO Make `keys.lock()` properly thread safe
+**** TODO Check for existing keys
+**** TODO Implement key validity timeout
+**** TODO Implement proper tests
+**** TODO Optionaly store key persistently between restarts
+
+*** Configuration [0/5]
+**** TODO Fix domain config
+**** TODO Make size of key configurable
+**** TODO Make key validity timeout
+**** TODO Make it possible to send emails over encrypted connections
+**** TODO Make html/text emails configurable
+
+*** Login Section (not sure if going to happen)