feat(opensmt): add abs function
fix(opensmt/parsers/smt2/CMakeLists.txt): dependency on smt2parser/lexer
fix(opensmt/parsers/smt2/CMakeLists.txt): suppress sign-compare warning
feat(opensmt/egraph/EgraphStore.C): remove sort check in mkEq

For now, we remove the requirement that

    "sort(LHS) = sort(RHS)"

. We still need to check LHS and RHS are Real/Int (or Int/Real).
feat(util/scoped_vec): make scoped_vec template
refactor(dsolvers): remove icp/ode solvers
refactor(realpaver): remove delta-related code

For the simplicity, I removed them. Later, we can add them back.
fix(util/scoped_env): add insert method, cbegin/cend
feat(dsolvers/nra_solver): implement incremental ICP
tests(c_api): add CMakeLists.txt
tests(c_api): add example_01
feat(opensmt/api): set verbosity/debug flags
feat(dsolvers/nra_solver): add '--stat' option

shows number of incomplete/complete checks
refactor(opensmt/smtsolvers): remove --short_sat option for now

will be added later
feat(opensmt/api): change C API to get lb/ub when make variable
feat(opensmt/api/OpenSMTContext): expose set method for verbose/debug
checkpoint