v0.7

PreciseSums 0.7

• Created a new non-binary linkage method with 'PreciseSumsPtr.h' in
  addition to 'PreciseSums.h'. To break binary package dependencies,
  the rxode2 internals use the function pointers, while the models
  built by rxode2 use the binary linkage.

• As requested by CRAN use strict headers.