add mask input mode

[lifubang]

As mentioned in redis/redis#6834
I try to add mask input mode to linenoise.
Add two functions:
linenoiseMaskModeEnable
linenoiseMaskModeDisable

And in ./linenoise_example
You can use /mask to enable input masking, and use /unmask to disable it.

Signed-off-by: lifubang lifubang@acmcoder.com

[itamarhaber]

Looks good to me - didn't test however ;)

[lifubang]

Looks good to me - didn't test however ;)

Thanks for your review.
You can use example.c to test.

lifubang@DESKTOP-3DDGGHK:/mnt/e/Develop/cc/linenoise$ ./linenoise_example 
hello> get mykey
echo: 'get mykey'
hello> /mask
hello> *********
echo: 'get mykey'
hello> *****
echo: 'hello'
hello> *******  # this is /unmask
hello> get mykey
echo: 'get mykey'
hello>

[antirez]

Merged and improved a bit in 4261898. Thank you.

[lifubang]

Thanks for your improved.
There is still a small bug, I have sent s fix PR, PTAL.