bug fix v0.6.4-with-no-mangle-double-dash

This is a bug fix release.

features changes:

• fix error refusing mangling double dash in global mode [#52]
• still refuse to mangle single dash [-] in global mode (not compatible with v0.6.1)
• now can mangle single-dash and double-dash in -G mode
• fix output bash empty array #53

internal changes:

• use Go 1.17.1 for compiling
• language_agnostic_tester.py re-write for python3
• sort argument key in Print_bash_args() Print_bash_global()
• sort input keys in docopts_test.go
• add PR #52 test to testcases.docopt
• completed developper's documentation
• #52 ignore [--] double-dash option in Print_bash_global()
• reformat of Go code with gofmt indent change Space ==> Tab
• add tests/functional_tests_docopts.bats