Improved Security; Cosmetic fix.

[jackrendor]

Tested and compiled on Fedora release 28 (Twenty Eight).

In this pull request I changed few things:

• Replaced getenv with secure_getenv. From the Linux Programmer's Manual:

  The secure_getenv() function is intended for use in general-purpose libraries to avoid vulnerabilities that could occur if set-user-ID or set-group-ID programs accidentally trusted the environment.

• Cosmetic fix. Just made a string that will contain the "help" message. In this way, it's easier to edit it. NOTE: Please, feel free to move that string where ever you like.
• Added the folder .vscode to the .gitignore to help who uses Visual Studio Code.

[cvengler]

Thank you for your PR! secure_getenv() is not working on macOS, is there an alternative which also works on Darwin ?

[cvengler]

According to the manual secure_getenv() is a GNU extension. so it isn't a standard function What do you think is it really essential to use secure_getenv().

[jackrendor]

I'm sorry to hear that. And I hope you can apologize me for being late. I'll make it execute secure_getenv instead of getenv only when compiling on Linux. Is it ok for you? I'll wait for your instructions before pushing.

[cvengler]

Can you show me a prototype of this ? If yes I'm fine with it.

[jackrendor]

Sure. I'll be happy to show it and explain it too.

• Line 7: Using #ifdef to identify platfrom (See How to identify platform/compiler from preprocessor macros? )
• Line 8: Using #define to replace getenv with secure_getenv whenever compiling on Linux. From the GCC GNU Docs:

  A macro is a fragment of code which has been given a name. Whenever the name is used, it is replaced by the contents of the macro.

• Line 33-34: Restoring getenv function.

[cvengler]

Sorry that it took me so long to answer. Thank you for your contribution to sysget. I will merge!

[jackrendor]

Do not worry about the delay! I'm happy you appreciated the edit! ^^ Happy Coding!