Fix handling of non-integer values

[eemeli]

I found this by chasing the source for an issue raised by @rxaviers here: eemeli/make-plural#2

In brief, there are incorrect comparisons in at least the functions mod() and _in() that make use of praseInt() rather than parseFloat(), which end up discarding the fractional part of the inputs, so we end up with:

$ ./src/cli.js 'n = 1' '1.1'
true

This does not match the syntax, which takes n as "absolute value of the source number (integer and decimals)" and defines the in_relation set by = as "only includes integers in the specified range".

I also added tests for the above, including the Latvian "zero" rule, as well as a test for '1.0' (correctly) failing i = 1 and v = 0.

[santhoshtr]

Thanks!