Run a linter over the code / normalize coding standards

[kberryUSGS]

Different numbers of spaces are used for indents, different curly-brace placements are used, snake_case vs. camelCase, etc... throughout the code.

[kberryUSGS]

Also, for exception error message variable names, we seem to alternate between msg, message, aMessage, etc... might as well use the same name.

[kberryUSGS]

Still needed: say in the README or contributing that we use the google style guide.

[oleg-alexandrov]

If linter checks are enabled, also a program should be provided to fix linter errors, such as clang-format-8, with a hook at commit time (the user installs the program separately and the git hook calls it). Or else developing code can be a very annoying affair, with sometimes hundreds of trivial things to fix manually for each commit.