Movement packets were handled incorrectly, because although the fields are specified as integers they are actually fixed-point values, which need to be converted to floating-point before use. These fields were converted with `as f64`, but they actually need to be scaled. To fix this add several new types, FixedPoint5 for 5-bit fractional fixed-point and FixedPoint12 for 12-bit. Both are parameterized by an integer type: FixedPoint5<i32> and FixedPoint5<i8> for 1.7.10/1.8.9, FixedPoint12<i16> for 1.9+. This moves the calculation into the packet field parsing, so it no longer has to be calculated in src/server/mod.rs since the scaling is taken care of as part of the field type. This fixes the long-standing invisible or actually misplaced players bug on 1.7.10 and 1.8.9, closes#139.
* Add new FixedPoint5<T> type for 1.7/8, https://wiki.vg/Data_types#Fixed-point_numbers
* Add FixedPoint12<i16> for 1.9+, moving type conversion into packet type
https://wiki.vg/index.php?title=Protocol#Entity_Relative_Move
* Add num-traits 0.2.6 dependency for NumCast to use instead of From
* Use FixedPoint5<i32> in spawn object, experience orb, global entity, mob, player, teleport
* Use FixedPoint5<i8> and FixedPoint12<i16> in entity move, look and move
* Update packet handling bouncer functions, using f64::from for each conversion
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