Add type-based DCT procedure names

[cval26]

Implements item 2 of #34.

Creates the following procedure aliases by overloading the existing DCT procedures, so that they can be called with names based on their DCT types (1, 2, 3). The following procedure aliases are created.

• dct_t1i and dct_t1 corresponding to dcosti and dcost;
• dct_t23i corresponding to dcosqi;
• dct_t2 and dct_t3 corresponding to dcosqb and dcosqf.

These correspond to the operations:

• initialize and perform DCT-1;
• initialize DCT-2, 3;
• perform DCT-2, 3.

[cval26]

@zoziha, this is now ready for review.

[zoziha]

Thank you for this @cval26 . Is there anything more to submit? If not, we can merge it.

[cval26]

We can merge this, @zoziha.