Add documentation to 'bitset_t' type class

# Version 0.0.1 [0.0.1D3 'Or Silver Boston']
# Changes in bitset_type.h and bitset_type.cpp
	+ Add std::vector<bool> 'bitset_t' constructor
	+ Overload const versions of
		- begin() and end() STL wraps
		- subscript operator[]
	+ Add both const and non-const versions of at() method
	+ Switch some constructor parameters to constant since they are not modified by
	these constructors
		- both initializer list constructors
		- both std::vector constructors
		- c-style boolean array constructor
	+ Switch some overloaded operators to constant ones since they don't modify
	the value of '*this'
		- unary complement ! and ~ operators
		- binary &, |, ^, NAND and NOR operators
		- assignment = operator
		- comparison == and != operators
		- relation >=, >, <=, < operators
		- stream insertion << operator
	+ Switch some methods' parameters to constant ones since they are not modified by
	these methods
		- both versions of resize method
		- fillWith() @value paramater
		- rotation and shift methods
		- @delimiter parameter of toBinaryString(std::string) method
	+ Switched some methods to constant since they don't modify `*this` value
		- both length() and size() methods
		- both toBinaryString() methods
	+ Switch some overloaded operators parameters to constant since they are not
	modified by these operators
		- binary &, |, ^, NAND and NOR operators
		- comparison == and != operators
		- @bits parameter of stream insertion << operator
# Changes in bitset_type.h
	+ Add Doxygen(c) documentation to 'bitset_t' file and class members
	+ Moved <iostream>, <algorithm> and <numeric> inclusions to implementation file
# Changes in bit_type.cpp
	+ Rewrite hammingDistance() method code since current one
		- does manipulate (which is bad) the parameters so lengths of bitsets
		are equal
		- uses O(n) extra space
		- runs much slower that it should be
	+ Rewrite rotation methods code since multiple test show that using STL rotating
	methods is slightly faster than traditional Knuth's triple-reverse algorithm
	+ Rewrite operator*() (scalar product calculation) method since curent one
		- uses O(n) extra space
		- does not work properly on some examples, must replace bitwise_xor()
		with bitwise_nequal() for obvious design reasons
		- multiple test show that using std::inner_product method achieves
		slightly better performance than using the combination of std::transform
		with std::accumulate
	+ Redesign equality/unequality tests operators since current ones
		- use O(n) extra space
		- multiple test show that using std::inner_product method achieves
		slightly better performance than using the combination of std::transform
		with std::accumulate
	+ Modify assignment operator code so it doesn't modify the @other parameter and
	can be declared constant
	+ Remove unneccesary commentary lines
	+ Modify multiple 'bitset_t' constructors to match C++ style
# Changes in bit_type.h and bit_type.cpp
	+ Add 'bit_t' copy constructor
	+ Improve 'bit_t' assignment operator
		- rewrite 'bit_t' assignment operator so it does not modify
		the @other parameter
		- switched assignment operator parameter to const since the operator does
		not modify the parameter anymore
# Changes in bit_type.h
	+ Add documentation to 'bit_t' copy constructor
	+ Replace NAND and NOR LaTeX symbols in documentation for \big\vert and \downarrow
	respectively
	+ Replace all occurences of 'inequality/not equal' by 'unequality/unequal' when
	reffered to unequality tests
# To do
	+ Think about relation operators overloading, or does that depend on the
	endianness
	+ Add proper documentation to newly and previously committed code
	+ Double check 'bit_t' and 'bitset_t' documentation
	+ Add more 'bitset_t' constructors