Lecture 04 and 05 updated

...cture_Notes/04_Vars_and_Exprs/lec_04_Vars_and_Exprs.ipynb

...d_Exprs/lec_04_Vars_and_Exprs_template_Gurmail_lec1.ipynb

...d_Exprs/lec_04_Vars_and_Exprs_template_Gurmail_lec2.ipynb

...ure_Notes/05_Using_Functions/lec_05_Using_Functions.ipynb

.../05_Using_Functions/lec_05_Using_Functions_template.ipynb

...ctions/lec_05_Using_Functions_template_Gurmail_lec1.ipynb

...ctions/lec_05_Using_Functions_template_Gurmail_lec2.ipynb