Move the custom types to a new subdirectory
Move the BCD type to its own directory
Change BcdSingle to SingleBcd
Change SingleBcd to FixedBcd

SingleBcd will be a single optimization of a FixedBcd value.
Complete the name change
Some cleanup
Reduce the exposure of the non-public template
Setup a package for the BCD types
Move common stuff to a shared module

Make sure the build of any of the modules in the BCD package
includes a reference to kuttaka/core.d or else a bunch of module
compilation issues will appear and cause compilation to fail.
This is the general outline for version one of the BCD types
Make FixedBcd useable again

Work still remains to be done to make convertBinaryToBcd more generic
and to get opOpAssign working again.

The straightforward constructor is purposely kept private and limited
to prevent use outside of local unit testing. And also to encourage the
use of the factory function bcd in package.d.

Improved the accuracy of other methods along the way, such as
isPackedBcd.

Also turned the constraint constants into templates. The goal is to
allow multiple integral types to be the payload backing type. This
should be able to expand beyond the built-in integral types with
the design proposed in this commit.
Get FixedBcd to compile again

Temporarily removed opOpAssign until it can be fixed.
Rework the BCD integral type to be unlimited in size
Add opSlice back in
Add back in toHash
Add opAssign back in

Instead of providing various opAssign overloads this time around
instead provide other ways to convert values to BcdInteger values.
Prove BcdInteger has the appropriate range interfaces
Add custom dup and idup properties
Merge pull request #179 from joichiro/types

Add a BCD integer