Build HTML files by default

[arvindpz]

Right now to generate HTML files from an epub file, we will do something like below

epub2sphinx -o sample -t classic   sample.epub                               # (Step 1)
cd sample                                                                    # (Step 2)
make html                                                                    # (Step 3)

With this change, (Step 1) will be enough to generate the HTML files. The HTML files will be generated even if the -b flag is not specified.

If -B flag is specified, the execution will stop without any post conversions.

In addition to this,

• included a change to ignore .tmp folder in the project
• refactored two methods in cli.py and convert.py
• minor style changes

[nifey]

Thanks for the PR. The changes look good.