Clean up the naming of examples

[podhrmic]

The tutorial example names are confusing - it goes as 0.c, slf1_basic_example.signed.c and so on.

Standardize the names, e.g. example_1.c...example_N.c, possibly with added explanation such as example_4_abs.c etc.

[bcpierce00]

Agreed that it is a mess at the moment. I'd rather have meaningful alphabetic names, though (i.e., abs.c, not example_4_abs.c), rather than number things in a single big sequence (which is much harder to manage as things get added, moved around, etc.).