Started to refactor the number tower

* Downgraded all arithmetic procedures, only small integers are
  processed.

* Removed test cases that are no longer applicable.

* Added type definitions of RFixreal, RFloreal and RComplex.
Added type registration and test code for RFixreal and RFloreal
Perform mpq_canonicalize when creating RFixreal
Added test case for writing RFixreal to output port
Removed unused smi_to_fixnum function
Added smi_to_fixreal
Splitted the new number tower code to finer_number.[ch]
Reordered several functions
Added r_fixreal_p and r_floreal_p
Added RComplex and several number functions

* Number reader test cases are splitted into separate test suite.

* Several old number functions are adapted to the new number tower, they
  would be fixed once the new number tower finishes.
Bug fix: #12

* Removed all global boxed objects, added them to RState, initialized during r_state_new.

* Added several helper macro to access fields of different number objects.
Added test coverage report support
Added lcov dependency to Travis-CI build process
Clears LCOV counters before each run of the test program
Updated test_compile teset suite to improve test coverage
Added allocator_disruptor to test allocation failure
Updated test_number test suite
Updated SConscripts to generate coverage report for ROSE only
Added code to more easily distinguish exact and inexact complex numbers.
Continued replacing the old number tower with the newer (and finer) one