Add length(), lengthT() and 'size' equivalents

[Red-Leader117]

Note: Fulfills issue #3

Adds the following Astr class function members:

• length()
• lengthT()
• size()
• sizeT()

Details:

• the "T" suffix indicates that the null-terminator is included in the returned
• size() and sizeT() are equivalents and are defined in terms of length*()
• length was chosen as the preferred names because a string is, for example, "5 characters long," while size may be interpreted as the number of bytes taken by the string

[Red-Leader117]

• size() and sizeT() must be tested
• const length?