Code cleanup: Remove unused functions

While iterfunc, itermap, iterfiltermap and the like were very useful
exercises for a beginning Python programmer, we're not actually using
them in the rest of our code. They closely duplicate the functionality
of the standard library's itertools.imap and itertools.ifilter, and/or
the functionality available in list comprehensions, and when we need
that functionality we're using the standard library functions. So this
code is taking up space for no current benefit.
Document a few more functions
Normalize function names to Python conventions
Improve readability of assignment statements

PEP 8 (http://legacy.python.org/dev/peps/pep-0008/) suggests spaces
around the = of assignment statements, after (but not before) the comma
of function calls, and around most binary operators. Further details at:
http://legacy.python.org/dev/peps/pep-0008/#other-recommendations
Consolidate vectorlength functions

There's no need for two vectorlength() functions, as we can deal with
inputs in any format (fontforge-style points, tuple-style points,
whatever). Consolidating these two functions makes the code cleaner.
Remove another unused function: ff_to_tuple

The only remaining use of ff_to_tuple was unnecessary, as it was
converting one Shapely object (LineString) into a list of tuples, which
was then passed to another Shapely object. Shapely is quite capable of
doing this conversion itself, so we can remove another function.
Remove another unused function

closestpoint_in_same_direction was part of an algorithm we've since
abandoned: it traced lines between midpoints by looking for the closest
point in the "same direction" as the incomplete line already traced,
where "same direction" was defined as "the angle shouldn't vary by more
than N degrees" (N defaulting to 30). That algorithm has since been
abandoned, and we're not going to go back to it -- the "find triangles
sharing a common side" algorithm works much better. So we can delete all
the code relating to the "closest point in same direction" algorithm.
Remove most commented-out code

There are a couple of abandoned approaches still lingering in
commented-out sections of code, but this is making it a bit harder to
identify functions that are truly unneeded. Deleting all the
commented-out code will make "orphaned" (unneeded) functions a little
more obvious, as they can now be identified by a simple text search.
Remove yet another unused function

The new_extraction_method function was the start of a rewrite of the
increasingly-misnamed extraction_demo function, which was starting to
look crufty. But instead of rewriting it, the correct approach is to
document it, change its name to something suitable, and remove the cruft.
Use more readable if-else expressions

Turn "if test: x=a else: x=b" into "x = (a if test else b)", which is
more readable in some cases, including this one.
Remove several more unused functions

Several more functions in extractpoints.py were remnants of the "find
the closest point in the same direction" algorithm, now abandoned. The
code is significantly easier to read with these functions removed.
Remove two more unused functions

get_glyph() was from an early version of the command-line interface, now
superseded. find_straight_lines() was from an early approach to finding
the glyph's "stroke width" (that is, the usual distance between parallel
sides -- or "parallel" curves -- of the glyph's outline). The approach
we're taking now uses Shapely to calculate the stroke width, and seems
much more reliable, so we can get rid of find_straight_lines() as well.
Remove an unused parameter

As suggested in the comment, the bounding_polygon parameter is
unnecessary with our new approach, so it's been removed to simpligy the
code still further.