Fixing problems with casing on keys in BindEnv and BindPFlag

Ran into an issue where I was utilizing camelcased names for keys (before I realized everything was ToLower()ed) and saw an bug where the keys inserted into the maps for env and flags wouldn't match the keys I was requesting.

As an aside - something that really perplexes me still - when I use: 
```go
BindEnv("eYEs")
```
in the test (not the key,ENVKEY way as in the pull request) somehow this test passes without the changes I made lowering the keys being inserted into the 'env' map. In my mental model of how this works from reading the code this should still fail... (but I'm quite a newb here with go)