Fix exportation directory issues + add exportation parameters (cover format and exportation directory)

[LeGoffMael]

• Fix exporting path missing / after the exporting directory for video and cover causing the final path to be /var/mobile/Containers/Data/Application/.../Library/Cachestrim.jpg instead of /var/mobile/Containers/Data/Application/.../Library/Caches/trim.jpg
• Fix the way to get the video file name during exportation to use path.basenameWithoutExtension(file.path) instead path.basename(file.path).split('.')[0] because when the file has a . in it name the final name is not correct
• Add parameter to specify exporting folder with outDir for video and cover exportation support for custom export outPath #40 (comment)
• Add parameter to specify the format of the cover to be exported (by default jpg)
• remove TODO comment because ffmpeg -y overwrite works properly
• display exported cover in example