Changes since version 0.2
-------------------------

Creation of a Deccoeff from a Python 3.0 str (i.e. unicode) instance
no longer goes through an intermediate bytes stage.

Add skeleton _Decimal class, to serve as base for Decimal, and
modify decimal.py to use it.

Make hash produce 64-bit values for 64-bit builds.

Convert source code to 4-space indent, no tabs

Use faster algorithm for basecase multiplication, minimizing the
number of divisions.

Add Karatsuba multiplication.

Add some profiling code for multiplication.

Add code to use 64-bit limbs (with 18 digits to a limb), if an
unsigned 128-bit type is available.

Fix bug in base conversion constants:  constants were swapped around
when LIMB_DIGITS == 4.

Fix bug in limb_getdigit:  it checks that n < 9;  should have been
n < LIMB_DIGITS

Fix rich comparisons to do type conversion.

Test-suite for deccoeff module added

Make limb types unsigned integers instead of signed integers.

Add telco benchmarking code.