Adding shell module
Adding shell module.
Adding a Readline finder CMake module because Readline is not in the default CMake module list.
Finding Readline.
Separating the 'task shell' command in a separate executable 'tasksh' and enabling command history traversal using GNU Readline
Separating the 'task shell' command in a separate executable 'tasksh' and enabling command history traversal using GNU Readline
Fixing tests and updating documentation.
Putting Readline code inside #ifdefs
Adding a man page and refering to it from other man pages
Porting on Ubuntu
Fixing some style issues.
Feature #328

- #328 Replaced the 'shell' command with a standalone 'tasksh' binary, which
  includes GNU readline support (thanks to Haitham Gad).