Display banner.txt on CLI command

[gmso]

Closes #50

Intro

Hi! :wave: I'm Germán, a Software Engineer based in Maryland. I really like this project's goal and ideas so I would like to contribute if possible.

Seeing as this is my first PR on this project, I went ahead and tackled issue #50, since it has the good first issue tag.

Changes

• Display the banner.txt when using the pushup command
• The banner is embedded into the executable
• The banner is not displayed when pushup -version is executed

Examples

$ pushup

        //                                                                  
     //  //      //////                        //                           
                //    //  //    //    //////  //////    //    //  //////    
               //////    //    //  ////      //    //  //    //  //    //   
              //        //    //      ////  //    //  //    //  //    //    
             //          //////  //////    //    //    //////  //////       
                                                              //            
                                                             //             

Usage: pushup [command] [options]

Flags:
 -version  Print the version number and exit

Commands:
 new [path]  create new Pushup project directory
 build       compile Pushup project and build executable
 run         build and run Pushup project app

$ pushup build

        //                                                                  
     //  //      //////                        //                           
                //    //  //    //    //////  //////    //    //  //////    
               //////    //    //  ////      //    //  //    //  //    //   
              //        //    //      ////  //    //  //    //  //    //    
             //          //////  //////    //    //    //////  //////       
                                                              //            
                                                             //             

$ pushup -version
Pushup 0.0.1

I hope I got the idea of this change right. If there are any suggestions or changes to be made, please let me know!