Eliminate use of undocumented Base.utf16_* functions (Fix #110)

[ScottPJones]

This package used two undocumented, unexported functions from base/utf16.jl.
This removes that dependency, which broke things when those functions were renamed.

[stevengj]

LGTM.

[stevengj]

Test failure:

while loading C:\projects\json-jl\test\runtests.jl, in expression starting on line 193 
ERROR: LoadError: test failed: "휒" == "𝜒"
 in expression: obj["𝜒"] == "𝜒

[IainNZ]

Its perfectly possible those things that were in the <= 0.3.0- block were broken, as that code path hasn't been tested in 1 year+.

[stevengj]

@ScottPJones, note that you should put (fixes #110) in the commit message, so that the corresponding issue is automatically closed (and cross-referenced) when this is merged. Also, a more specific commit message would be nice, e.g. eliminate use of undocumented Base.utf16_* functions (fixes #110).

[ScottPJones]

Yes, I know that, just rushing to get this fixed, sorry!

[ScottPJones]

@IainNZ You were correct, I shouldn't have relied on those old functions (they didn't cast to UInt32 before doing the << 10, and lost the top bits). They looked almost identical to what was in utf16.jl,
but looks can be deceiving!

[IainNZ]

Heh, yeah. I figured your Unicode-foo would know what the right thing to do was, hopefully Travis agrees!

[ScottPJones]

Now, if somebody can merge this, so I don't annoy people trying to use JSON 😢!

[IainNZ]

Waiting for CI to go green

[ScottPJones]

Smart man! Thinking about it, I wonder if the old code just bit rotted. Did unsigned values used to end up as UInt, like signed values? I tripped over when I started in Julia because of the fact that unsigned values go from UInt8, UInt16, UInt32 instead of UInt)

[IainNZ]

Not sure

[IainNZ]

Tagging now

[stevengj]

Yes, in old versions of Julia, integer arithmetic promoted to Int/UInt.