Simple API for programmatic access to migrations and direct queries

Added `Migrator` class for simple and easily readable programmatic access to migrations (it's a facade for the library). Interfaces of a few other classes are wrapped too, to make API simpler and more *fluent*.

In addition to usual methods like `MigrateUp` and `Rollback`, it contains a query class for making direct queries to the database, without recording migrations history. This part of API can be seen as a complement to @markrendle's Simple.Data. Together with FluentMigrator, they provide both DML and DDL.

To be most useful, a new NuGet package should be added with FM, FM.Runner and FM.API.

Example code with migrations:
```csharp
using (var migrator = new Migrator()
    .LoadMigrations(typeof(DataMigration).Assembly)
    .OpenConnection("SqlServerCe", "...")) {
    migrator.MigrateUp();
}
```

Example code with direct queries:
```csharp
using (var migrator = new Migrator().OpenConnection("SqlServerCe", "..."))
using (var query = migrator.GetQuery()) {
    query.Create.Table("Users")
        .WithColumn("Id").AsInt32().PrimaryKey().Identity()
        .WithColumn("Name").AsString()
        .WithColumn("Email").AsString();
}
```