add a few macros and functions

[FAReTek1]

This pr just adds a few macros/functions that i thought would be useful

• zfill from python in string.gs - just pad in 0s to the front of a string until it's the given width
• logb - log with base - not sure which way to put parameters
• sign macro, (x > 0 - x < 0)
• atan2, taken from wikipedia
• dir macro, which is similar to the point to x/y from one of the recipes
• i added these to the testing project, although there are some false 'positives' due to floating point error

[FAReTek1]

i removed it then

[FAReTek1]

bump

[aspizu]

shouldn't this be -1?

[FAReTek1]

last one should be. ill change it

[FAReTek1]

I now realise that making a pull request means that one should check through the code for obvious mistakes. i found another issue where the logb macro was tested, but it was previously removed, for example.

i have checked through all the code. I think that I tested it at the time. However, due to floating point error, the test script might not be fully accurate. maybe a rounding to ~3dp would be ideal