Stylistic refactoring

[Paalon]

There are some inconsistent styling in the source code (e.g. indent by 4 spaces vs 1 tab character, etc.). We should use something consistent.

[Paalon]

JuliaFormatter will be fine. I made a configuration for YAML.jl:

# .JuliaFormatter.toml
# Formatting options for the default style supported in JuliaFormatter v1.0.56.
# https://domluna.github.io/JuliaFormatter.jl/stable/

# style = "default"
# indent = 4
# margin = 92
always_for_in = "nothing" # default false
# for_in_replacement = "in"
whitespace_typedefs = true # default false
# whitespace_ops_in_indices = false
remove_extra_newlines = true # default false
# import_to_using = false
# pipe_to_function_call = false
# short_to_long_function_def = false
# long_to_short_function_def = false
# always_use_return = false
whitespace_in_kwargs = false # default true
annotate_untyped_fields_with_any = false # default true
# format_docstrings = false
# align_struct_field = false
# align_assignment = false
# align_conditional = false
align_pair_arrow = true # default false
# conditional_to_if = false
# normalize_line_endings = "auto"
# align_matrix = false
# join_lines_based_on_source = false
trailing_comma = true # default false
# trailing_zero = true
# indent_submodule = false
# separate_kwargs_with_semicolon = false
surround_whereop_typeparameters = false # default true
# variable_call_indent = []
# short_circuit_to_if = false

remove_extra_newlines = true and trailing_comma = true are my preferences. Other options are

1. to follow the existing YAML.jl's code as far as possible or
2. defaults of DefaultSyle of JuliaFormatter or
3. to follow JuliaLang/julia's convention.