replace JSON with 1.5.1

[Watson1978]

Like CRuby, I replaced the JSON with 1.5.1 which distributed in http://flori.github.com/json/

[lrz]

Nice work! I have a couple questions:

1. what does this new JSON implementation bring compared to the current one? Is the current one not good or does not conform to CRuby?

2. is there a test/spec suite that we can use to check if it works as expected? I'm quite worried about memory management, because MacRuby's GC is different, and C extensions can sometimes not work properly or can leak memory under MacRuby.

[Watson1978]

Thank you for your comment :)

1. This implement will solve,

1. fix a #1275 "JSON library outdated or broken"
2. Cost of the maintenance will decrease. currently implement is MacRuby original.
   I think what somebody of MacRuby Team continues maintaining all the time will be high cost.

2. unit test exists in "test/test-mri/test/json/test_*.rb"
   The test seemed to work well.

[lrz]

OK, I agree, please go ahead and merge! Thanks for the work :)

[Watson1978]

Thank you!
I merged.