Updated unit tests for TextFileReaderTest to use a ivar for the file path names.

Implemented a set of ivars in TextFileReaderTest to use as the file paths throughout the entire unit test.
Added TextFileReaderTest unit test and updated header method in TextFileReader to handle negative numbers

A set of unit tests were added for TextFileReaderTest to handle valid arguments, negative numbers, and floats. There were also modifications to the TextFileReader header method to handle a negative argument for numLines.
Updated unit test to account for too many lines requested and too large of starting positions.

The unit tests were updated to account for a user requesting to start reading the file beyond the number of lines in the file. It also now accounts for a user asking for more lines than are in the file.
Unit tests for TextFileReaderTest testFooter and modifications to TextFileReader footer method.

Added unit tests for TextFileReaderTest testFooter method to test normal requests, negative numbers, floats, and requesting too large of a file.

Modifications to the TextFileReader::footer method now provide appropriate counting so we get the lines we want. The previous implementation moved the lines requested up by one so if you were looking for lines 8 and 9 it would return lines 7 and 8.
Added unit test for TextFileReaderTest::testNumberOfLines

Added the unit test for TextFileReaderTest for testing the number of lines in a file.