Bug fixes, LSP, and debugger improvements

[smarr]

This PR combines a few minor fixes with some improvements for LSP support and debugging:

Debugger

• added support for transmitting arrays partially (i.e., indexes 0 to 100, 400 to 550 etc, as used by some IDEs)

LSP Support

• added getters to query information
• use SSymbol for variables as well, ensures consistency with all other constructs (@Richard-Roberts this is something we briefly discussed)
• added interface for message sends (Send) to get their selector
• allow overriding selector() to make sure source sections can be handled properly

Bug fixes:

• added missing specialization for #== prim
• make sure loop frequency is never larger than 1.0
• catch all throwables when loading a module

[coveralls]

Coverage decreased (-0.02%) to 79.828% when pulling f78cd8f on lsp-improvements into 302f297 on dev.

[coveralls]

Coverage decreased (-0.02%) to 79.828% when pulling 7f93924 on lsp-improvements into 302f297 on dev.