Getting started with chapter 5.
Renaming of programs for Chapter 5 and adding chapter 5 files.
Update Ex_5.10_exprcmd.rst
Update sec_4.3.rst
Added exercise 5.15, 5.16, 5.17
Header for program
Explain the operation
Added exercise 5.18
Added exercise 5.19
Added exercise 5.20
Explaination for 4.4
Update

* Ex_4.4_rpn_top_two_elements.rst
* Ex_4.12_recursive_itoa.rst
* Ex_4.6_calculator_variables.rst
* Ex_4.13_reverse_string.rst
Finished explaining 4.4
Completed Exercise 4.7

Update Ex_4.12_recursive_itoa.rst
Update Ex_4.12_recursive_itoa.rst
Exercises 4.8, 4.9, 4.10 and 4.11
Programs 4.9,4.10,4.11
Added chapter 6 to index
* Added a sample template program
* Update Ex_5.2_getfloat.rst
* Ex_5.2_getfloat.c
* 1.2_Example java from Java 8 Spec
Templates for

* Exercise 5.6
* exercise 5.7
* exercise 6.1
* exercise 6.2
Update Ex_5.3_strcat.c and Ex_5.3_strcat.rst
Templates for Exercise 6.3 and 6.4
Update Ex_5.4_strend.rst and Reformatting Ex5.4_strend.c (work in
progress)
Incomplete exercises 6.5 and 6.6
In progress Ex5.5