[suggestion] Data structures, and number handling

[rtheunissen]

Hi there, I would like to ask about these topics before I spend the time to write them up.

1. Data Structures

• Arrays
• SPL Data Structures (potentially mentioned in the SPL section?)
• The data structures extension, php-ds

2. Number handling

• float
• bcmath
• gmp
• The decimal extension

Do you think that these are viable topics of discussion in the guide?