Add xmodem library

[gilman88]

No description provided.

[github-actions]

Arduino Lint has suggestions for possible improvements to https://github.com/gilman88/xmodem-lib:

Linting library in xmodem-lib
INFO: No header file found matching library name (XModem_transfer_library.h). Best practices are for primary header     
      filename to match library name.                                                                                   
      See: https://arduino.github.io/arduino-cli/latest/library-specification/#libraryproperties-file-format            
      (Rule LS008)                                                                                                      
WARNING: Potentially misspelled extras folder name found: xmodem-lib/extra                           
         See: https://arduino.github.io/arduino-cli/latest/library-specification/#extra-documentation
         (Rule LS011)                                                                                
WARNING: library.properties name value XModem transfer library is longer than the recommended length of 16 characters.
         See: https://arduino.github.io/arduino-cli/latest/library-specification/#libraryproperties-file-format       
         (Rule LP010)                                                                                                 
WARNING: library.properties name XModem transfer library contains spaces. Although supported, best practices is to not  
         use spaces.                                                                                                    
         See: https://arduino.github.io/arduino-cli/latest/library-specification/#libraryproperties-file-format         
         (Rule LP015)                                                                                                   
WARNING: Library name XModem transfer library contains "library". This is superfluous.                         
         See: https://arduino.github.io/arduino-cli/latest/library-specification/#libraryproperties-file-format
         (Rule LP016)                                                                                          

Linter results for project: 0 ERRORS, 4 WARNINGS

-------------------

Linting sketch in xmodem-lib/examples/Basic_Receive
WARNING: Sketch file/folder name mismatch. The primary sketch file name must match the folder: Basic_Receive.ino
         See: https://arduino.github.io/arduino-cli/latest/sketch-specification/#primary-sketch-file            
         (Rule SS001)                                                                                           

Linter results for project: 0 ERRORS, 1 WARNINGS

-------------------

Linting sketch in xmodem-lib/examples/Basic_Send
WARNING: Sketch file/folder name mismatch. The primary sketch file name must match the folder: Basic_Send.ino
         See: https://arduino.github.io/arduino-cli/latest/sketch-specification/#primary-sketch-file         
         (Rule SS001)                                                                                        

Linter results for project: 0 ERRORS, 1 WARNINGS

-------------------

Linter results for projects: 0 ERRORS, 6 WARNINGS

[github-actions]

Your submission has now been accepted! Thanks for your contribution to the Arduino Library Manager index.

The library(s) will be available for installation via Library Manager within a day's time.

You can check the logs from the Library Manager indexer for your library(s) here:
http://downloads.arduino.cc/libraries/logs/github.com/gilman88/xmodem-lib/