feat: update build system

We have "build.sh" script which builds both the SMT solver written in
C++11 and tools written in Ocaml. After the build, it copies all the
binaries to "bin" directory.
feat(bin/dReach): move dReach to bin directory
test: use "solver" instead of "dReal" in tests
feat(bin/dReach): use real_path to follow symlink in finding SCRIPT_PATH
feat(DSL/): basic code generation
fix(tools/DSL): update bouncing ball benchmark
chore(tools/DSL): remove OASIS generated file
fix(tools/DSL): rename datatypes

 - ASSIGN1/2 => ASSIGN
 - RealVar2 => BRealVar
chore(tools/DSL): reorder targets in Makefile
chore(tools/Makefile): remove dReach from tools (it's in bin now)
fix(dsolvers/ode_solver): handle a corner case where m_ode_list/m_var_list is empty

Closes #2
fix(dsolvers/ode_solver): handle a corner case where m_ode_list/m_var_list is empty