added sizedefinitions for Texas_PWP_R-PDSO-G20

Created by: s-light

added HTSSOP-20-1EP_4.4x6.5mm_P0.65mm_EP3.4x6.5mm_Mask2.75x3.43mm (Texas_PWP_R-PDSO-G20)

please let me know if the size addition is fine this way. i have used the custom_name_format to make sure that the sizes in the name correspond to the actual sizes used in the definition.

for this footprint i would like to have a hand-soldering variant - means i would add a mask on the bottom side - this way you can reflow the part with a normal soldering iron from the other side. (i tried this out several times with this chip and it works really nice) should i add this variant myself in form of manually copieng the thermal-via variant - or is this concept fair enough to be incorporated in the script itself?