use done_testing() instead of plan(), so that tests specific to some compile flags could be implemented
basic implementation for int64_type
Merge branch 'master' into kazuho/experiments/int64

Conflicts:
	picojson.h
simplify the code (calls to both const and non-const versions of get<double>() convert int64 values to double)
add doc
add boundary tests for int64_t
fix boundary handling of int64_t
run test with int64_t support as well
fix build error on linux w. PICOJSON_USE_INT64
Merge branch 'kazuho/experiments/int64'