Add transactional I2C to changelog and remove misplaced entry in alpha.2

Author: eldruin

CHANGELOG.md

@@ -8,7 +8,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ## [Unreleased]
 
 ### Added
-- `Transactional` SPI interface for executing groups of SPI transactions
+- `Transactional` SPI interface for executing groups of SPI transactions.
+- `Transactional` I2C interface for executing groups of I2C transactions.
 
 ### Changed
 
@@ -20,7 +21,6 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Added
 - 10-bit addressing mode for I2C traits.
 - `try_set_state` method for `OutputPin` using an input `PinState` value.
-- `Transactional` interface for grouping SPI transactions
 
 ### Changed