Add umbrella header file that matches lib name

[sebromero]

Solves #3 by adding an umbrella header that matches the library name as desired by Arduino Lint.
The old header is left in place for the time being to ensure backwards compatibility. To avoid clashes in sketches using this library, they can now refer to this new header file.

[github-actions]

Memory usage change @ 0888c22

Board	flash	%	RAM for global variables	%
arduino:mbed_nicla:nicla_vision	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:mbed_portenta:envie_m7	N/A	N/A	N/A	N/A
arduino:renesas_portenta:portenta_c33	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0

Click for full report table

Board	examples/BasicUsage flash	%	examples/BasicUsage RAM for global variables	%	examples/ReadWriteRegs flash	%	examples/ReadWriteRegs RAM for global variables	%
arduino:mbed_nicla:nicla_vision	0	0.0	0	0.0	0	0.0	0	0.0
arduino:mbed_portenta:envie_m7	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A
arduino:renesas_portenta:portenta_c33	0	0.0	0	0.0	0	0.0	0	0.0

Click for full report CSV

Board,examples/BasicUsage<br>flash,%,examples/BasicUsage<br>RAM for global variables,%,examples/ReadWriteRegs<br>flash,%,examples/ReadWriteRegs<br>RAM for global variables,%
arduino:mbed_nicla:nicla_vision,0,0.0,0,0.0,0,0.0,0,0.0
arduino:mbed_portenta:envie_m7,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A
arduino:renesas_portenta:portenta_c33,0,0.0,0,0.0,0,0.0,0,0.0

[aentinger]

LGTM 👍