Guideline for shell/environment variable in Stdlib functions

[CymDeveloppement]

In issue #355 and #351 I suggest the use of shell/environment variable. this is interesting for modify default comportement or interact with script with a config file.
I think it's important that we have guidelines for stdlib function that uses shell variables.

My first Idea is :

variable that use in more than one function (global) :
AMBER_{VAR_NAME}
example :
AMBER_VERBOSE AMBER_TMP_DIR AMBER_APP_NAME

variable that use in a specific function
{FUNCTION_NAME_IN_UPPER_CASE}_{VAR_NAME}
for example i work on a depends function that can install package if a shell variable exist
DEPENDS_INSTALLER

the config file can be :

AMBER_APP_NAME="myInstaller"
AMBER_VERBOSE=3
DEPENDS_INSTALLER="sudo apt install "