Bugfix: avoid replacing "/home/user-alt" by "~-alt"

Add escaped backslashes so as to replace the "/home/user/" string in the path by "~/"
Add case for screen title escape chars
Suppress double escape in screen title
Add more generic test for screen/byobu/tmux title
Revert "avoid replacing "/home/user-alt" by "~-alt""

Doesn't work in home folder as $HOME and $PWD don't have any trailing "/".
This reverts commit 4a64c6ccec5efe49e2feb7a78dff556638088093.
bugfix #107: zsh-compatible if statement

An if statement was used without the conditional operator: if [[ "" ]]
This patch adds one: if [[ ! -z "" ]]
Making the code zsh compatible.
Replace lptag by prompt_tag

prompt_tag is more consistent with the other prompt_* functions.
Differents colors for differents hosts you SSH in

Adds the LP_ENABLE_SSH_COLORS option to use a numeric hash of the hostname as the displayed color.