benchmarks(simple): add ChemE benchmark (disjunct)
feat(dsolvers/icp_solver): add rp_problem display for debugging
feat(src): use namespace dreal
feat(util/hexfloat): add hexfloat to print exact/hexdecimal rep. of double number

 - std::hexfloat should do the job. However current g++ does not support
   it yet[1].
 - Instead, we use "%a" format specifier[2] + snprintf.

[1]: http://gcc.gnu.org/onlinedocs/libstdc++/manual/status.html
[2]: http://www.cplusplus.com/reference/cstdio/printf/
checkpoint
fix(realpaver/rp_variable): rp_union_display_simple gets "out" param
feat(realpaver): make realpaver as c++ code-base
feat(src/util): add interval class, use in scoped_env
fix(dsolvers/icp_solver): use util/interval in icp_solver
feat(util/interval): add constructor interval(rp_interval)
feat(realpaver): use util/interval in proof