use dscanner to replace phobos style_lint_shellcmds

[Nicholas Wilson]

Phobos does a bunch of style checks with grep, it would be good to do those with dscanner instead (partly so we can ignore the etc. directory.

https://github.com/dlang/phobos/blob/master/posix.mak#L589

Things phobos checks with grep

• Check for trailing whitespace
• Enforce whitespace before opening parenthesis
• Enforce no whitespace after opening parenthesis
• Enforce whitespace between colon(:) for import statements (doesn't catch everything)
• Check for package wide std.algorithm imports
• Enforce Allman style
• Enforce do { to be in Allman style
• Enforce no space between assert and the opening brace, i.e. assert(
• Enforce space after cast(...)
• Enforce space between a .. b
• Enforce space between binary operators

I'm sure that Dscanner does most of these but if any are missing, that would be good to add.