solves issues #4 and #9

[CIPHERTron]

• added a webpage which converts CGPA to GPA i.e. gpa.html
• gpa.js contains the javascript for gpa.html
• separated script from index.html and added it to index.js

[CIPHERTron]

@sriharikareddy2 @shruti170901, please take a look at this PR and suggest changes!