Support for OOK_PWM and OOK_PPM modulations and reading from file in sendook

[albymor]

Dear Evariste, I added two functionalities to sendook:

1- add support for OOK_PWM and OOK_PPM modulations (see for reference rtl_433). These are useful if you have to emulate some wireless temperature sensor

2- add support for reading bit and duration from a file. The file format is the same as RFA files supported by rpitxV1 [frequency active, duration (ns), padding]

73' Alberto IZ3QBR