Collatejson: handle special character in strings.

BugID: CBIDXT-276
- added unit test case SpecialString to simulate this bug.

Performance profile.
  BenchmarkDecode-8  1000000 2935 ns/op   552 B/op 14 allocs/op (before)
  BenchmarkDecode-8   500000 7379 ns/op  1785 B/op 42 allocs/op (after)

Change-Id: Ida881c263e416f6696b2884fb6fcd3df73ba6fc2
Reviewed-on: http://review.couchbase.org/43892
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Pratap Chakravarthy <prataprc@couchbase.com>