Table CSS for SRFI documents

[Lassi Kortela]

Should https://srfi.schemers.org/srfi.css have some default styles for 
<table> tags? The default defaults are not that convenient since table 
cells have no visible borders. I've used something like this:

table {
  border-collapse: collapse;
}
table, td, th {
  border: 1px solid black;
}
We could also reserve the styling for <table class="table"> so as to not 
disrupt existing tables relying on the HTML defaults:

table.table {
  border-collapse: collapse;
  border: 1px solid black;
}

table.table td, th {
  border: 1px solid black;
}