Revert PR #171 which auto decodes URL parameters
Request to roll back commit a03b5be0b72f1a686b6ca594c145cee665e6db7b which implemented PR #171 which fixed Issue #159.

## Scope
The commit changed the behaviour the template `@` used to access URL parameters and is noted as a `Breaking change`. The change auto-decodes the URL parameter using `decodeUrl()` regardless of the parameter-type.

Exact change: https://github.com/dom96/jester/pull/171/files#diff-6a259fda1df185e57d46cf13c94d178eb6be365815acdf3dc8a132ab58a63f61L640-R640

## Problem
When using Javascript to perform POST-request the data will/could be wrongly decoded. 

Basic examples, but imagine this being Base64, JSON or other encoded data:
```javascript
# A1
fetch("/api", {
  method: "POST",
  body: new URLSearchParams({ msg: "My message with plus+++signs" })
});
```
```javascript
# A2
$.ajax({
  type: "POST",
  url: "/api",
  data: { msg: "My message with plus+++signs" }
});
```
```nim
import jester
routes:
  post "/api":
    echo @"msg"
    # Actual: My message with plus   signs
    # Expected: My message with plus+++signs

```

When parsing the the above POST-request with Jester the parameters will be returned after the `decodeUrl()` and therefor stripped for the `+`-signs, which in this case is required.


**Actual**
`My message with plus   signs`

**Expected result**
`My message with plus+++signs`
 

## Suggestion
Roll this commit back and let the URL param be parsed by the end user. In some cases they need to be parsed as traditional URL parameter (`example.com?project=hello`) or as Form data provided by a Javascript function.

1. Roll back the commit
2. Provide a compile option to opt out

If accepted then I'll be happy to provide the PR.