Missing std.manifestJson and incorrect description of std.manifestJsonMinified in doc/ref/stdlib.html

[RadxaYuntian]

I just want a simple function to output a Json file. stdlib.html told me there are either std.manifestJsonEx or std.manifestJsonMinified for me to choose. But you really have to look at std.manifestYamlDoc to know that there is actually a 3rd std.manifestJson function, which doesn't need any additional parameters, and prints in nice formatting.

Also the explanation of std.manifestJsonMinified is broken, which reads Under the covers, it calls std.manifestJsonEx:'). That's not a valid function call.

[johnbartholomew]

Thanks for reporting the missing docs! Fixed by #1154