Include argument to set root node

[LiamSkirrow]

There should be a way to specify a known module in the design as the root node, such that this module is treated as the starting point. For example, for a given hierarchy like so:

altTop
└── mod2  
    └── mod1  
        └── mod3  
            └── mod4

Running verilogtree -f rtl/simple/*v -top mod1 should give:

mod1
└── mod3  
    └── mod4  

[LiamSkirrow]

This would also be useful just for general everyday use. If you want to print out a hierarchy but you don't know specifically which files to include to generate the hierarchy, you could simply just do a find . -name *.v and chuck that into verilogtree, then just specify the top level module you want to look at and verilogtree won't print out all the irrelevant modules.

[LiamSkirrow]

This ticket is almost complete, but I'd like to add some text down the bottom for specified top-level modules, to remind the user that the hierarchy they're viewing is modified and may not include all the modules in the design... Something like: "Using user-specified top-level modules: mod0 mod1 mod2" etc

[LiamSkirrow]

Should also create an example for this argument in the man page. Ex: verilogtree -f $(find . -name *.v -printf '%p ') --no-inst-name --top mod0 mod1

mod0
├── mod3  
│   └── mod4  
└── mod1  
    └── mod3  
        └── mod4  

mod1
└── mod3  
    └── mod4