Move cache from lib/sqlbuilder to internal/.

internal/cache/cache.go

internal/cache/cache_test.go

internal/cache/hashstructure/LICENSE

internal/cache/hashstructure/README.md

internal/cache/hashstructure/hashstructure.go

internal/cache/hashstructure/hashstructure_test.go

internal/cache/hashstructure/include.go

internal/cache/interface.go

internal/sqladapter/database.go

lib/sqlbuilder/exql/default.go

lib/sqlbuilder/exql/hash.go

lib/sqlbuilder/exql/interfaces.go

lib/sqlbuilder/exql/statement.go

lib/sqlbuilder/exql/template.go

lib/sqlbuilder/template_test.go

mysql/template.go

postgresql/template.go

ql/template.go

sqlite/template.go