revlog: improve documentation of the entry tuple
The code in revlog, and outside revlog directly use the index's entry tuple,
with direct integer indexing. This is a voluntary trade off to obtains better
performance from the Python code at the expense of the developers sanity.
Let's at least have a clear and central documentation about what this tuple is
about.
Differential Revision: https://phab.mercurial-scm.org/D10643
{
// Enforcing
"eqeqeq" : true, // true: Require triple equals (===) for comparison
"forin" : true, // true: Require filtering for..in loops with obj.hasOwnProperty()
"freeze" : true, // true: prohibits overwriting prototypes of native objects such as Array, Date etc.
"nonbsp" : true, // true: Prohibit "non-breaking whitespace" characters.
"undef" : true, // true: Require all non-global variables to be declared (prevents global leaks)
// Environments
"browser" : true // Web Browser (window, document, etc)
}