[Breaking] Remove dmlc::Parameter

[hcho3]

Extracted from #285.

• Do not use dmlc/parameter.h.
• CompilerParam no longer inherits from dmlc::Parameter. Consequently, it now implements a special method ParseFromJSON() that ingests parameters from a JSON string.
• Now parameters are set with JSON strings.
  Before:

CompilerHandle handle;
TreeliteCompilerCreate("ast_native", &handle);
TreeliteCompilerSetParam(handle, "quantize", "1");
TreeliteCompilerSetParam(handle, "parallel_comp", "100");
TreeliteCompilerSetParam(handle, "native_lib_name", "predictor");

After:

CompilerHandle handle;
const char* params = "{\"quantize\": 1, \"parallel_comp\": 100,"
                     " \"native_lib_name\": \"predictor\"}";
TreeliteCompilerCreateV2("ast_native", params, &handle);

• Breaking: The C API functions TreeliteCompilerCreate and TreeliteCompilerGenerateCode are renamed to TreeliteCompilerCreateV2 and TreeliteCompilerGenerateCodeV2, respectively, to indicate the different calling signature. In addition, TreeliteCompilerSetParam has been removed.
• Add C++ tests to test the correctness of ParseFromJSON().
• Upgrade Google Test framework to 1.11.0 to test the content of exceptions.

[codecov]

Codecov Report

Merging #293 (8bfcbb4) into mainline (5d7d968) will decrease coverage by 0.78%.
The diff coverage is 100.00%.

@@              Coverage Diff               @@
##             mainline     #293      +/-   ##
==============================================
- Coverage       84.78%   83.99%   -0.79%     
  Complexity         46       46              
==============================================
  Files             101      102       +1     
  Lines            7899     7909      +10     
  Branches           50       50              
==============================================
- Hits             6697     6643      -54     
- Misses           1177     1241      +64     
  Partials           25       25              

Impacted Files	Coverage Δ
include/treelite/c_api_error.h	100.00% <ø> (ø)
include/treelite/compiler.h	100.00% <ø> (ø)
include/treelite/compiler_param.h	100.00% <100.00%> (ø)
python/treelite/frontend.py	76.69% <100.00%> (-0.25%)	⬇️
src/c_api/c_api.cc	97.09% <100.00%> (+0.43%)	⬆️
src/compiler/ast_native.cc	96.09% <100.00%> (+0.01%)	⬆️
src/compiler/compiler.cc	96.36% <100.00%> (+23.63%)	⬆️
src/compiler/failsafe.cc	86.82% <100.00%> (+0.12%)	⬆️
tests/cpp/test_compiler_param.cc	100.00% <100.00%> (ø)
python/treelite/contrib/msvc.py	0.00% <0.00%> (-67.15%)	⬇️
... and 16 more

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[trivialfis]

I think JSON handles this automatically.

[hcho3]

No, the None object gets serialized to null.

[trivialfis]

Got it, the param is optional.