start working on reorganizing headers and splitting them (update issue #226)
 - create one file per public feature 
 - split gmsh.hpp, functionspace.hpp
 - move options to feel/options.cpp
 - remove some .cpp files that were dealing with program_options
move BDF coefficients to bdf class and cleanup
use TSBase as base class update issue #237
Merge branch 'develop' into feature/header

Conflicts:
	feel/feeldiscr/functionspace.hpp
rename header for operations(*,+,/,-) in variational formulations
update issue #226
update issue #226
Merge branch 'feature/header' of https://github.com/feelpp/feelpp into feature/header

# Please enter a commit message to explain why this merge is necessary,
# especially if it merges an updated upstream into a topic branch.
#
# Lines starting with '#' will be ignored, and an empty message aborts
# the commit.
fix compilation update issue #226
update issue #226: work on tutorial to reduce compilation time
Merge remote-tracking branch 'origin/develop' into feature/header

Conflicts:
	feel/feeldiscr/functionspace.hpp
	feel/feeldiscr/projector.hpp
update issue #226: add domain.hpp
call start to update bdf coefficients (update issue #237)
@StephaneVeys updated test_bdf2 (arguably a simpler version)
a+=m was too much
added more precision
@StephaneVeys update test to verify bdf implementation
fix indentation
update issue #237
 - introduce bdf->priorTimes() to initialize bdf, see
 testsuite/feeldiscr/test_bdf2 for an example
 - change behavior of order change, use directly bdf order but requires
 initialization of priorTimes()
fix compilation (update issue #226)
fix compilation (update issue #226)
fix execution of sound
update
update(simpler and use #226) and fix execution