Refactored to build the full crontab manually

[jamesrwhite]

Should resolve:

• https://github.com/jamesrwhite/minicron/issues/165
• https://github.com/jamesrwhite/minicron/issues/109
• https://github.com/jamesrwhite/minicron/issues/74
• https://github.com/jamesrwhite/minicron/issues/73

..still working on this.

[jamesrwhite]

Merging this as is, seems to be working pretty well from what I can tell. Will be released as part of 0.9 most likely as it's a big change.

[xakraz]

Thx