uuid: use plain package instead of module

[DifferentialOrange]

Using separate module instead of plain package introduced several
issues related to dependencies inside the repository (see #134).
At the same time, same functionality could be provided with package.
The only drawback is that google/uuid will be included in main
package dependency even if user decide to use custom UUID parser or
ignore UUID completely.

Closes #134

[DifferentialOrange]

If UUID is not included, UUID is not supported (thus decoders and encoders are not set):

go test uuid_test.go 
--- FAIL: TestSelect (0.00s)
    uuid_test.go:103: UUID select failed: Supplied key type of part 0 does not match index part type: expected uuid (0x12)
    uuid_test.go:75: Response Data len != 1
panic: runtime error: index out of range [0] with length 0 [recovered]
	panic: runtime error: index out of range [0] with length 0

goroutine 19 [running]:
testing.tRunner.func1.2({0x579b80, 0xc00018e060})
	/usr/local/go/src/testing/testing.go:1209 +0x24e
testing.tRunner.func1()
	/usr/local/go/src/testing/testing.go:1212 +0x218
panic({0x579b80, 0xc00018e060})
	/usr/local/go/src/runtime/panic.go:1038 +0x215
command-line-arguments_test.tupleValueIsId(0xc000083520, {0x0, 0x0, 0x55a220}, {0xc8, 0xf0, 0xfa, 0x1f, 0xda, 0x29, ...})
	/home/georgymoiseev/Development/github/tarantool/go-tarantool/uuid_test.go:78 +0x1c6
command-line-arguments_test.TestSelect(0xc000083520)
	/home/georgymoiseev/Development/github/tarantool/go-tarantool/uuid_test.go:108 +0x2b7
testing.tRunner(0xc000083520, 0x594960)
	/usr/local/go/src/testing/testing.go:1259 +0x102
created by testing.(*T).Run
	/usr/local/go/src/testing/testing.go:1306 +0x35a
FAIL	command-line-arguments	0.005s
FAIL

To test it, you'll need to move uuid_test.go to main folder, rename package from uuid_testto tarantool_test (otherwise Go will not run them) and comment _ "github.com/tarantool/go-tarantool/uuid" import.

We may add a negative test (UUID is not supported if import not added), but I'm not sure we need it.

[Totktonada]

Thanks! I don't see any downsides.