Some fixes and additions

[danmandle]

• ADDED: The option to set a temp directory for the ebook parts
• ADDED: The option to set a file path to kindlegen instead of requiring to be in PATH for people with permission issues or wanting to keep it in their repo.
• ADDED: Custom date for the issue.
• FIXED: Date of the issue displayed on the Kindle.
• FIXED: Path resolution.
• UPDATED: README with all of the above.
• CHANGED: Underscores instead of truncated spaces in title/filename.

[moszeed]

rly great! ... i'm open for more :) ...