Fix writing for simple types like true,false,null,undef

[sirkrypt0]

Previously, writing simple types was not in line with the CBOR standard. Writing the array [false,true,null,undefined] would result in 84 38 54 75 96 which is totally off. This is now fixed and correctly returns 84 f4 f5 f6 f7, which can be decoded correctly.

Closes #4

[demetriopitasi]

Works also for me