Log Message:
Update to 1.6

Upstream changes:
1.6
 - Add parse_json() wrapper that does not guess if a string is actually a file/url
 - Fix a few rchk warnings (mostly false positives)
 - Add asJSON method for hms
 - Do not require is.vector() for unbox to support values with attributes e.g. \ 
factor or tzone
 - write_json now suppresses recoding of strings on windows, fixes #226
 - Hide internal libyajl symbols from shlib
 - Remove C calls R connection API which are no longer allowed on CRAN. This may
   lead to about 5% performance decrease for parsing from connections.
 - Remove depreacted rbind.pages function