Bump version to 0.1.5

- Simplify the interface to explicitly support epub, pdf and mobi format
- Remove the following options from CLI
  * remove --exc-words
  * remove --inc_words
  * remove --ignore-case
  * remove --non-exts
- Update gemspec to include files explicitly without using git
- Update 'code_lister' to 0.0.9
- Update 'thor' to 0.19.1
- Code cleanup and refactoring
- Remove list of changes from README.md to CHANGELOGS.md