There are currently several Params and case related issues floating around in Hugo.
This is very confusing for users and one of the most common support questions on the forum.
And while there have been done some great leg work in Viper etc., this is of limited value since this and similar doesn't work:
`Params.myCamelCasedParam`
Hugo has control over all the template method invocations, and can take care of all the lower-casing of the map lookup keys.
But that doesn't help with direct template lookups of type `Site.Params.TWITTER_CONFIG.USER_ID`.
This commit solves that by doing some carefully crafted modifications of the templates' AST -- lowercasing the params keys.
This is low-level work, but it's not like the template API wil change -- and this is important enough to defend such "bit fiddling".
Tests are added for all the template engines: Go templates, Ace and Amber.
Fixes#2615Fixes#1129Fixes#2590
This commit replaces the multuple `bytes.Containts` and `bytes.Replace` with a custom replacer that does one pass through the document and exploits the fact that there are two common prefixes we search for, `src=` and `href=`.
This is both faster and consumes less memory. There may be even better algos to use here, but we must leave some room for improvements for future versions.
This should also make it possible to solve #816.
```
benchmark old ns/op new ns/op delta
BenchmarkAbsUrl 25795 22597 -12.40%
BenchmarkXmlAbsUrl 17187 11166 -35.03%
benchmark old allocs new allocs delta
BenchmarkAbsUrl 60 33 -45.00%
BenchmarkXmlAbsUrl 30 16 -46.67%
benchmark old bytes new bytes delta
BenchmarkAbsUrl 5844 4167 -28.70%
BenchmarkXmlAbsUrl 3754 2069 -44.89%
```
Fixes#894
