parameters: renamed defaults
parameters: improved the parameter class:

delay of error messages, renaming
parameters: added generation of help from defaults with proper formatting
parameters: corrected typos in opaque_object
parameters: added doc (to be reread)
Add parameters in solver : draft

- added parameters (include, and so on).
- but still what is the best practice here remains unclear.
parameters: renamed defaults
parameters: added doc (to be reread)
Add parameters to pytriqs
adding function to produce aligned output
inlined function for formatted output
stack_trace : default is non gdb

gdb requires a special setting on linux and
does not work on mac (and it is slow on linux if we need
to catch a lot).

Reversing the default : define TRIQS_STACKTRACE_WITH_GDB
to use gdb for the stack_trace