v0.3

• fixed compilation error
• removal of the hep::mpi_single_generator function. This is now on by
  default - the integration results are independent of the number of processes
• temporary fix for single-precision floating point numbers that are 1.0f
  and therefore outside of the half-open interval [0,1)
• changed hep::vegas_pdf interface to use more descriptive member function
  names and moved the member function icdf outside the class
• revamped documentation
• changed function names of hep::cumulative_result and
  hep::chi_square_dof to the same names with a 0 and 1 at the end
  of their names; 0 uses the same algorithm as before, 1 weighs all
  results equally. The function hep::cumulative_result remains but requires
  an additional argument
• added new global configuration function hep::vegas_cuba_refinement()
  that can be used to modify pdf refinement to use CUBA's method
• removed --enable-tests configure switch. All external dependecies are
  gone and running make check is sufficient now to run tests
• changed interfaces hep::cumulative_result and hep::chi_square_dof
  which no longer need to be called with the numeric type; the type is
  automatically determined by the iterators
• support for MPI can now be enabled with --enable-mpi independently from
  the examples. If MPI is enabled, the MPI examples are built if examples are
  activated and the MPI tests are checked if tests are activated. The MPI
  headers are installed in any case because MPI must be explicity requested by
  including hep/mc-mpi.hpp
• renamed hep::linear_grid to hep::vegas_pdf and moved code from VEGAS
  into this class
• add more unit tests, use Google Test as testing framework
• improved the MPI VEGAS example
• added new hep::mpi_single_generator function that adds the possibility to
  use the same random numbers for MPI and non-MPI routines. This makes
  hep::mpi_vegas return the same numerical result as hep::vegas
• fixed integer overflow bug on 32-bit architectures that caused VEGAS' grid
  adjustment to fail when the number of calls surpassed 2^16
• modified VEGAS callback functions to return a boolean variable signaling to
  stop all remaining iterations
• modified the verbose callback function to print the error in percentage