lib: don't show the ".md" extension when listing the topics.
lib: implemented the `create` command.

Note that it doesn't actually persist yet.
Be more explicit when the command is failing because of the passed parameters.
Fixed the wrongArguments function output.
Typo.
lib: updated the value for some constants.

Moreover I've moved the "dirName" constant out as a global variable. This will
be useful for the test suite.
lib: implemented the `push` command.

Note that this command doesn't persist yet.
lib: implemented the `delete` command.
lib: use the "dym" package for the delete command.
lib: implemented the `rename` command.
lib: polishing.
lib: implemented the last remaining functions.
lib: added the utils.go file.

This file basically has all the utility functions that were scattered around
the "lib" package.
lib: added tests for the utils.go file.