[docs][llvm-symbolizer] Improve llvm-symbolizer documentation

As detailed in https://bugs.llvm.org/show_bug.cgi?id=42253, there were a
number of issues in the llvm-symbolizer documentation. This patch fixes
them by:

 1. Adding [addresses...] to the synopsis, and matching the formatting
    of other tools.
 2. Rewriting the description to fix grammar issues and mention other
    usage options.
 3. Rewriting the examples to be easier to read.
 4. Re-ordering the options into alphabetical order.
 5. Improving the text of some of the option descriptions, and adding
    some examples to individual options.
 6. Splitting the Mach-O options into a separate section of the
    document.
 7. Standardizing on double dashes for long options throughout the file.
 8. Adding a reference to the llvm-addr2line document.

Reviewed by: mtrent, ikudrin

Differential Revision: https://reviews.llvm.org/D63651

llvm-svn: 364410