Support for std and no_std environments

[gabhijit]

Right now most of the scalpel code works assuming std environment. However, there is no real reason why the same code cannot be adopted for no_std environment. At least following needs to be kept in mind

1. Use of hashbrown instead of std::collections::HashMap for no-std environments
2. Use of lock_api in place of std::sync::
3. Defining crate::Error compatible with no_std environment

For now for ease, let's simply restructure the use statements such that parts can be std and no_std and then add those one by one.

[csking101]

Hi sir, can I take this up?

[gabhijit]

I believe this is a bit involved. Let me create another issue, to use OnceCell, you may want to work on that. After that we can visit that. Fixing that will anyways be required.

[csking101]

Sure, that'd be great!