Clean up and improve command line handling

This fixes fixes a crash when FuseSoC was launched without arguments
and finally makes it possible to get information about plusargs by
specifying --help after the name of the core for FuseSoC simulations
(e.g. fusesoc sim wb_intercon --help)
simulator/verilator: add defines_files directory to include_dirs

Without this, the automatically generated define header file
can't be found by the verilator source files.
section/verilator: add $(SYSTEMC)/include to include dirs

Also, only add the SYSTEMC_INCLUDE environment variable to
the include dirs if it's set.
section/verilator: fix build_SysC launcher

The sources can be found in src_root/core/src_file, update
the build_SysC launcher to reflect this.
verilator: use pr_info when compiling cores

Signed-off-by: Franck Jullien <franck.jullien@gmail.com>

Conflicts:
	fusesoc/section/__init__.py
	fusesoc/simulator/verilator.py
verilator: add src_root in included dirs

Signed-off-by: Franck Jullien <franck.jullien@gmail.com>
coremanager.py: Simplify add_cores_root
Update .gitignore to ignore autoconf files

Do not consider autogenerated files to be part of the potential files to
be tracked.
Remove trace output

Remove old traces. If you want to trace the execution do something like:
'python -m trace -t bin/fusesoc'
Ignore swap files

The Worlds Best Editor (TM) uses swap files, do not consider them in git
Do not catch exceptions on from().

Before any Attribute error would silently throw away the exception and
show the --help. Now it crashes with a trace as is expected.
No arguments should work for python3 as well
Remove fake provider interfaces.

Moved logic to instantiate providers from __init__.py.
Removed Provider interface class.
Move Section from it's own directory

Section can just as well be a normal file, make it so.
Remove factory pattern and use self registration instead.
Fix Makefile.am after section dir got purged