Improve RTL spacing classes

[KareemDa]

My idea is to use:

• "Start -> s" instead of "Left-> l"
• "End-> e" instead of "Right-> r"

and internally, tailwind will detect the direction and add "right" or "left" class

this can be applied to:

• margin
• border
• padding
• text-align

[KareemDa]

Using this guideline, if we're building a multi-directional website and want to add margin before text:

we can use: ms-2 instead of ltr:ml-2 rtl:mr-2

[thibaudcolas]

See #1483 which discusses this extensively. Logical properties and values are a concept in CSS itself, no need for Tailwind itself to reinvent this.