Progressive embedding

See merge request !53

function now is static

This reverts commit 73cd204b.

Revert "Merge branch 'gmm5.4-compat' into 'master'"

See merge request !52

This reverts merge request !50

GMM 5.4 compat

See merge request !50

cf https://github.com/getfem-doc/getfem/commit/06165410f54c1c82ee82903906c6497cd535ce83

# Conflicts:
#	CMakeLists.txt

Move CMAKE_INSTALL_INCLUDEDIR after inclusion of GNUInstallDirs

See merge request !49

when CoMISo is one target, part of a larger project, we want to use
the "current" binary directory, and not the general one, where
everything would be mixed up

before inclusion, CMAKE_INSTALL_INCLUDEDIR is empty so the command
target_include_directories does not include the right directory

Cleanup ipopt solvers

See merge request !48

removing redundant IPOPTSolver implementation

APIADD: intermediate callback can be specified with
void set_callback_function
(std::function<bool(const IPOPTCallbackParameters &)>)

APICHG: renamed NProblemIPOPT -> IPOPTProblemInstance
since it does not implement the NProblemInterface and should not be
used by clients of CoMISo directly

this allows string literal parameters to decay to std::string implicitly

APICHG: rename getters to use get_ consistently

unify method signature formatting
cleanup whitespace
obey 80 character limit