Remove trailing whitespaces
Slightly change header description and clean up help printing message
Drop all profiles management

Also drop the ~/.sackrc sourcing. I think all config values should be
env. variables.
Remove the long whitespaces variable 'sack__file_name'

Replace it by an empty string variable in the 'display_shortcuts' function.
Remove the 'sack__OS' option

Prefer using the 'uname' command.
Improve regexp to remove escape char: can take 3 parameters

Two or three parameters can be passes to ag for instance to specicify some
colors : foreground, backgroud and a style such as underline or bold.
Write 'open at line' Bash script in a dedicated file

Prefer using environment variable than a config file.
Drop the 'on the fly' creation of the 'open at line' script

Also introduce the SACK_COLORS environment variable. If it's not defined, the
code still works.
Fix SACK_COLORS

Test if the string is empty. SACK_COLORS can be a list of colors params such as
'--color-line-number=1;35;40 --color-path=1;34;40' etc.
Remove trailing whitespaces in the README file
Update the install script
Update the README file

* add a section about the legacy code
* remove all sections about profiles management
* add a section about the three (optional) env. variable for sack minimal configuration
Remove the '.sackrc' file
Update the README file about the SACK_EDITOR variable
F script: fix the EDITOR variable
Fix the print help function and 'sack_config' sourcing

Also remove a comment about profiles.
Fix SACK_COLORS test: wrong conditional expression.

Replace '-z' by '-n' to test if the string is non-empty.
Fix SACK_SHORTCUT test variable

There is no '$' prefix.