add a new input parameter to control the decimal precision

[changhuixu]

Propose:

This directive will accept an optional input parameter: decimalPrecision.

• The parameter decimalPrecision is a number. Default is 0, which will not take effect. If the value is a number other than 0, then it must be a positive integer. Otherwise, if negative, assign a value of 0; if not integer, assign its floor integer.
• The parameter decimalPrecision will take effect only when decimal is true.
• If the number of digits equals the decimalPrecision, then prevent typing/pasting/dropping.

[changhuixu]

in the end, this is done by checking the pattern attribute. See demo page for examples.