Tweak formatter output for readability (#26)

[nllong]

Closes #26.

Implements the three formatting tweaks requested in the issue (ported from the lbl-srg/modelica-buildings PR #2426 post-processing script directly into the formatter, so they apply by default with no extra step):

1. Single-argument calls stay on one line

A function call with exactly one argument keeps its argument inline instead of breaking it onto its own line, so common wrappers like pre(x), der(y), sin(z) and sum(a .* b) stay compact. Calls with two or more arguments are unchanged. Handled at the AST level for both regular (function_call_args) and external (external_function_call_args) calls, so nested multi-argument calls still break correctly.

2. Blank line before section headers

A single blank line is inserted before equation/initial equation, algorithm/initial algorithm, and public/protected section headers to separate them from the preceding declarations. A trailingNewlines counter ensures the blank line is not duplicated when -extra-padding already added one.

3. Tidy revision docstrings

The stray empty line frequently left between the final </ul> and </html> of a revisions docstring is removed (</ul>\n\n</html> → </ul>\n</html>), preserving the original tag casing and </html> indentation.

Example

  Real p;

initial equation
  y=pre(x);

equation
  z=der(y);
  p=sin(x)+atan2(
    x,
    y);

Tests / docs

• New tweaks.mo fixture + golden output exercising all three tweaks, added to the example-file test table.
• New unit test TestCollapseRevisionListBlankLine covering single/multiple blank lines, preserved indentation, case-insensitivity, and no-op cases.
• Regenerated the affected golden .mo/.mot files; every diff is an intended single-arg collapse or section blank line.
• Updated README.md (new "Default formatting behavior" section) and CHANGELOG.md.

make all (build + test) passes.