[GSOC 2014][JSON] refactor the output code to support JSON format

[yangmin zhu]

Hi everyone,
I learned a lot about git from the great book [1] and I had cleared my
repository in github[2].
I splited my current work into 3 commits:
1. Add basic hook framework for JSON output and the support for '-j' option. [3]
2. Modify sys_read(),sys_write() in io.c to use this hook framework. [4]
3. Add a very simple test to show the result. [5]

The most important part is in [3], I modified tprints() and tprintf()
in strace.c to support hook framework. And you can find 2 simple
example in [4] to get familiar with how to modify the current code to
use the hook framework.

I will do more on test. I think I can write a small program(in Python
or C) to parse the JSON output and translate the output to the
original format. We can then compare the translated output to the raw
output as a check.

Currently I'm using the hook to implement the JSON output and It seems
works good. But I'm not sure whether it has any potential big problem
in the future or maybe conflict with something else in strace?

[1] http://git-scm.com/book/
[2] https://github.com/zym0017d/strace_GSOC/
[3] https://github.com/zym0017d/strace_GSOC/commit/e52637b4ca7536bb1259f6850df774357e8102f2
[4] https://github.com/zym0017d/strace_GSOC/commit/759f3a3d145f72a82fa981187de4b3d5154fbec3
[5] https://github.com/zym0017d/strace_GSOC/commit/d84de67753cc228b619ec3e6d97bc1c59278918f

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YangMin