Using banner disables usage & synopsis

Nobody has claimed this yet.

Example option block :

```
opts = Trollop::options do
version 0.1

usage "foo|bar"
synopsis "Reticulate splines"

banner "Recognized options: "
opt :dry_run, "Don't do anything", short: "-n"
end
```

Output when passed `--help` is :
```
Recognized options:
-n, --dry-run Don't do anything
-v, --version Print version and exit
-h, --help Show this message
```

If I comment *just* the banner line, I get this :
```
Usage: test foo|bar
Reticulate splines

0.1
Options:
-n, --dry-run Don't do anything
-v, --version Print version and exit
-h, --help Show this message
```

Additionally, I get warnings (the shebang line is `#!/usr/bin/env ruby -W`) depending on whether the `usage` or `synopsis` lines are comment out :
```
$gem-path/trollop-2.1.2/lib/trollop.rb:480: warning: instance variable @usage not initialized
$gem-path/trollop-2.1.2/lib/trollop.rb:481: warning: instance variable @synopsis not initialized
```

Reproduce the issue with the Ruby option block shown in the report, comparing output with and without the banner line and with usage or synopsis commented out. Trace how banner, usage, and synopsis are handled when --help is rendered, then ensure the usage and synopsis remain available and the uninitialized-variable warnings are resolved.

Written by the indexing model from the issue text.