fobos single building mode

This kind of fobos file should have only one building mode defined by the section [default], e.g.

[default]
help      = This is the help message...
colors    = True
quiet     = False
jobs      = 1
compiler  = custom
fc        = ifort
modsw     = -module
mpi       = False
cflags    = -c -cpp -O2
lflags    = -O2
preproc   = -DPROFILING
libs      = lib/bar.so lib/boo.a
include   = other_include_path another_include_path
inc       = .cmn .icp
mod_dir   = ./mod/
obj_dir   = ./obj/
build_dir = ./
src       = ./src/
exclude   = pon.F cin.f90
mklib     = static
log       = False
target    = foo.f90
output    = FoO

Note that due to the design-idea of this kind of fobos file, only one default mode should be defined, but if other modes (sections) are defined, only the one named default is used, whereas the others are ignored. Moreover, the default mode can be placed everywhere into the file, it is not requested to be the first mode defined. Finally, if there is no section named default an error message is prompted, e.g.

Error: fobos file has not "modes" section neither "default" one