A major change the the API was made in `v8` to seperate concerns between the different SQL statement types.

**Why the change?**

1. There were feature requests that could not be cleanly implemented with everything in a single dataset.
2. Too much functionality was encapsulated in a single datastructure.
    * It was unclear what methods could be used for each SQL statement type.
    * Changing a feature for one statement type had the possiblity of breaking another statement type.
    * Test coverage was decent but was almost solely concerned about SELECT statements, breaking them up allowed for focused testing on each statement type.
    * Most the SQL generation methods (`ToInsertSQL`, `ToUpdateSQL` etc.) took arguments which lead to an ugly API that was not uniform for each statement type, and proved to be inflexible.

**What Changed**

There are now five dataset types, `SelectDataset`, `InsertDataset`, `UpdateDataset`, `DeleteDataset` and `TruncateDataset`

Each dataset type has its own entry point.

* `goqu.From`, `Database#From`, `DialectWrapper#From` - Create SELECT
* `goqu.Insert`, `Database#Insert`, `DialectWrapper#Insert` - Create INSERT
* `goqu.Update`, `Database#db.Update`, `DialectWrapper#Update` - Create UPDATE
* `goqu.Delete`, `Database#Delete`, `DialectWrapper#Delete` - Create DELETE
* `goqu.Truncate`, `Database#Truncate`, `DialectWrapper#Truncate` - Create TRUNCATE

`ToInsertSQL`, `ToUpdateSQL`, `ToDeleteSQL`, and `ToTruncateSQL` (and variations of them) methods have been removed from the `SelectDataset`. Instead use the `ToSQL` methods on each dataset type.

Each dataset type will have an `Executor` and `ToSQL` method so a common interface can be created for each type.

# Conflicts:
#	HISTORY.md
#	sql_dialect_test.go