Add encryption/, bootstrap des project.

algorithms/encryption/(README.md, des/)
	-Add `encryption/` dir with a brief README, for encryption
	projects.
	-Bootstrap the `des` project: add boilerplate makefile, source
	files, etc.
Add test module, func headers to des.h.

algorithms/encryption/des/src/(des.(c, h), test.c)
	-Add a `test` module, to contain the project's executable's main
	entry point so that the `des` module remains standalone code
	that can be easily compiled into another project.
	-Forward declare `DES_encipher()` and `DES_decipher()` in
	`des.h`.
	-Define dummy, placeholder `DES_encipher()`.
Define bit-operation helper functions.

algorithms/encryption/des/src/des.c
	-Define `_setBit()`, `_getBit()`, and `_shiftDist()`, which will
	help with all of the bit operations that DES requires.
Add documentation comments to the des module.

algorithms/encryption/des/src/des.(c, h)
	-Add documentation comments to `Byte_t`, `_setBit()`,
	`_getBit()`, `_shiftDist()`, and `_printBinaryBytes()`.
Bootstrap bit_ops sub-project.

algorithms/encryption/bit_ops/(README.md, makefile, src/bit_ops.(c, h))
	-Bootstrap the `bit_ops` subproject of the `des` project.
	-Add boilerplate makefile, source files.
	-Add placeholder README.
Add test module. Add function prototypes.

algorithms/encryption/bit_ops/src/(bit_ops.(c, h), test.c)
	-Add a `test` module, to contain the project's compiled
	executable's main entry point.
	-Add prototypes for all of the `bit_ops` module's necessary
	functions to `bit_ops.c`; some are commented out, to suppress
	compiler warnings.
Define BitOps_getBit()/BitOps_printBits().

algorithms/encryption/bit_ops/src/bit_ops.(c, h)
	-Define `BitOps_getBit()`; use it to define
	`BitOps_printBits()`.
	-Add documentation comments to each.
Redefine BitOps_getBitString() to return a char *.

algorithms/encryption/bit_ops/src/bit_ops.(c, h)
	-Redefine `BitOps_getBitString()` to return a `char *`, instead
	of writing the binary string to `stdout`, for
	testability/greater modularity.
Add tests/helper macros to the test module.

algorithms/encryption/bit_ops/src/test.c
	-Define helper function-like macros `DEF_UNIT_TEST()` and
	`EXEC_UNIT_TEST()`.
	-Define unit-tests for
	`BitOps_getBit()`/`BitOps_getBitString()`.
Add documentation comments to test module.

algorithms/encryption/bit_ops/src/test.c
	-Add documentation comments to macros/functions/file header.

makefile
	-Compile in `libtap`.
Define BitOps_setBit().

algorithms/encryption/bit_ops/src/(bit_ops.h, test.c)
	-Define, document, and test `BitOps_setBit()`.
Define BitOps_rotLeft().

algorithms/encryption/bit_ops/src/bit_ops.(c, h)
	-Define and document `BitOps_rotLeft()`.
Define a unit-test for BitOps_rotLeft().

algorithms/encryption/bit_ops/src/test.c
	-Define a unit-test for `BitOps_rotLeft()`, itself implemented
	in 73fa6e5.
Merge branch 'algorithms/encryption.bit_ops' into algorithms/encryption.des

algorithms/encryption/bit_ops/
	-Implement a lightweight bit-operations library.
Remove bit-operations code from des module.

algorithms/encryption/des/src/des.(c, h)
	-Remove all functions that governed extended bit operations, as
	they're now implemented in the `bit_ops` mini-library.
	-`#include` said lib.
Compile in the bit_ops mini-library.

algorithms/encryption/des/makefile
	-Add a target and recipe to compile the `bit_ops` mini-library
	implemented in `../bit_ops` (see c04d7c0).
Define DES-specific 28-bit _rotLeft().

algorithms/encryption/des/src/des.c
	-Define `_rotLeft()`, because DES requires that its left
	rotation operates on the first 28-bits of a byte array, so
	`BitOps_rotLeft()` wouldn't work (as it operates on entire bytes
	at a time, and would thus have to select between 24 and 32).
Implement permuted block

algorithms/encryption/des/src/des.c
	-Implement generation of the first permuted key, and its
	seventeen permuted blocks.
Implement subkey generation.

algorithms/encryption/des/src/des.c
	-Implement subkey generation (via permuted choice 2) in
	`DES_encipher()`.
Specify BitOps_getBitString() bytes arg as const.

algorithms/encryption/bit_ops/src/bit_ops.(c, h)
	-Declare `BitOps_getBitString()`'s `bytes` argument as `const`,
	because it shouldn't be modified.