Adding support for CritBitTree

[georgelemon]

Adding support for std/critbits is easy

jsony/src/jsony.nim

Lines 11 to 13 in 4fa3a9b

	type
	SomeTable*[K, V] = Table[K, V] | OrderedTable[K, V] |
	TableRef[K, V] | OrderedTableRef[K, V]

To be changed to

type
  SomeTable*[K, V] = Table[K, V] | OrderedTable[K, V] |
    TableRef[K, V] | OrderedTableRef[K, V] | CritBitTree[V]

[treeform]

Can you make a PR?