Support grid() args in tpar

[grantmcdermott]

Closes #235.

pkgload::load_all(("~/Documents/Projects/tinyplot"))
#> ℹ Loading tinyplot

op = tpar(grid.col = "hotpink", grid.lty = "solid", grid.lwd = 2)
plt(0:10, pch = 19, grid = TRUE)

tpar(op) # reset defaults
plt(0:10, pch = 19, grid = TRUE)

^{Created on 2024-10-29 with reprex v2.1.1}