Define project style guide

[keanutaufan]

As for now, this project does not follow any style guide nor it defines its own style guide. Decisions regarding this issue has to be made so that every algorithm and data structure implementations is coded consistently so that it can be read and maintained easier.

Considerations for now:

• Use an already-existing and well known style guide so that a new guideline does not have to be made
• Use Doxygen to generate documentation right from the source code
• For template class, write both the declaration and definition in the header file instead of separating it into .hpp and .ipp files

After a proper style guide is established, this repository can accept pull requests for new DSA implementation.