Require mutable reference if method changes device state

Previously, all methods that access a Nitrokey device took a reference
to the device as input.  This method changes methods that change the
device state to require a mutable reference instead.  In most case,
this is straightforward as the method writes data to the device (for
example write_config or change_user_pin).  But there are two edge cases:
- Authenticating with a PIN changes the device state as it may decrease
  the PIN retry counter if the authentication fails.
- Generating an HOTP code changes the device state as it increases the
  HOTP counter.

1 files changed, 1 insertions, 0 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 718b796..e98e857 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -37,6 +37,7 @@ SPDX-License-Identifier: MIT
 - Use mutability to represent changes to the device status:
   - Implement `DerefMut` for `User<T>` and `Admin<T>`.
   - Add `device_mut` method to `DeviceWrapper`.
+  - Require a mutable `Device` reference if a method changes the device state.
 
 # v0.3.4 (2019-01-20)
 - Fix authentication methods that assumed that `char` is signed.