Add rounding functions + small fixes

[GlitchlessCode]

The Suggestion

Add the following functions:

• round(x)
• floor(x)
• ceil(x)

  Implementation description

• Added the functions
• Ensured same formatting and error checking to the original codebase
• Included IMP-DOC for new functions
• Updated README to add gm:round, gm:floor, gm:ceil to list of functions

  Additional changes

• Fix small typo in gm:arctan2 IMP-DOC
• Define math entity in load

[gibbsly]

looks good to me, interesting ceil implementation

[GlitchlessCode]

Yeah, the ceil was kinda bizarre, cause the only form of rounding (at least that I'm aware of) that is built in to MC is flooring. So, floor(x) is just floor(x), and round(x) is floor(x+0.5), but ceil(x) has to be -floor(-x)

[gibbsly]

yea I know of a floating point hack round but no ceiling, the only thing I can think of is doing like floor(x+(1-min_double)) but even then i'm not sure