Issue Description:

swift package init --help

OPTIONS:

--type empty|library|executable|system-module

Provide `package init ` option to allow custom name:

--packageName provide custom package name

Alternatively, we would provide a naming strategy based on the folder name. This is more involved an perhaps not needed if a custom name could be provided.

Provide `package init ` option to allow specifing the casing of the package name. Currently this is locked to `self.pkgname = dirname`. All my folder are snake case but all my package names are PascalCased.

--nameStrategy default|camelCase|PascalCase|snake_case

Since it seems to be convention to name packaes with Pascal case then we probably just need

--nameStrategy default|PascalCase

where default is the current verbarim of the name of the folder

1) We would guess if the source name is snake_case, camelCase or PascalCase

snake_case: no uppercase chars, _ or -

camelCase: first char lowercaase, some uppercase

PascalCase: first char uppercase some uppercase and lowercase letter.

2) If the name has any spaces, go back to default and print a message.

If we cant naively figure out on of the three cases above then just give up and go back to default.

Sample code:

https://github.com/apple/swift/blob/master/stdlib/public/SDK/Foundation/JSONEncoder.swift

```

fileprivate static func _convertFromSnakeCase( stringKey: String) -> String {...}

fileprivate static func _convertToSnakeCase( stringKey: String) -> String {...}

```