Add cd/pwd commands and relative path support

[reveever]

Add

• cd - change current directory (validates path exists and is a folder)
• pwd - show current directory

Support for relative paths with . prefix in all commands (mkdir, ls, rm, etc.)

Example

./onedrive-uploader cd /Documents
./onedrive-uploader pwd
./onedrive-uploader ls .
./onedrive-uploader mkdir ./NewFolder