Ciphersweet

* `CompoundIndex` has been updated to allow "row transformations" which are more arbitrary than the standard `Compound` transformation, but ultimately, combine multiple columns into a single output string.
* If you elect to use a custom row transformation and it returns a string, it will omit the typical `Compound` transform. To continue using `Compound` after-the-fact, return an array instead.
* New interface: `RowTransformationInterface` which extends the standard `TransformationInterface`
* New Transformations added:
* `AlphaCharactersOnly`
* `FirstCharacter`
* To improve efficiency, `EncryptedRow` now allows you to just call `getBlindIndex($name)` to calculate the values for a single desired index.
* The documentation has been improved to address repeat sources of end user confusion about the features and limitations of this library.

* Fixes a bug with `EncryptedField` ignoring the pre-hash plaintext transformations. See 22.

* Fixes a bug with `EncryptedRow` ignoring the pre-hash plaintext transformations.
* Don't auto-suggest `ModernCrypto` on old platforms.

Created an `EncryptedRow` API, which allows the simple creation of blind indexes composed of multiple fields (a.k.a. `CompoundIndex`).

The new API's basic usage is [documented](https://github.com/paragonie/ciphersweet/tree/master/docsencryptedrow).

* Mostly, documentation fixes.
* Also, added the [Compound](https://github.com/paragonie/ciphersweet/blob/master/src/Transformation/Compound.php) transformation, which is useful for packing together multiple indexes.

Stable release of CipherSweet. The only changes since `v0.2.0` are documentation-related.