implement #346
 - add option gmsh.npartitions
 - add option gmsh.respect_partition to ensure that the partitioned
   mesh will be  read completely
fixed #346
 - implement an example that reads a partitioned mesh and retrieve the first
 element of each partition @asamake
implement ioption to read integer options
implement -rd option that enables Relwithdebinfo
Merge branch 'develop' of https://github.com/feelpp/feelpp into develop