Styleguide compliance with respect to integer types.

Fix #140.
Changes:
`Multivector` template parameter `unsigned int rank` → `int rank`:
> do not use unsigned types to say a number will never be negative. Instead, use assertions for this.

Formatting function argument `unsigned char const precision ` → `int const precision`:
> Of the C integer types, only int should be used. When appropriate, you are welcome to use standard types like size_t and ptrdiff_t.
We use int very often, for integers we know are not going to be too big, e.g., loop counters. Use plain old int for such things. You should assume that an int is at least 32 bits, but don't assume that it has more than 32 bits. If you need a 64-bit integer type, use int64_t or uint64_t.