[ViralBShah]

This modernizes IniFile.jl and prepares the 0.6.0 release. It started from evaluating IniFile for Circuitscape.jl, which reads INI files written for Python's ConfigParser. The parser now follows Python's configparser. On a file of edge cases (multi-line values with blank and comment lines, indented keys, delimiters, and inline comments on and off) it gives the same results as Python 3's configparser.

Fixes

• Short entries such as a= were dropped, because every line shorter than 3 characters was skipped. Now only blank lines and comments are skipped.
• Malformed lines were printed to stdout with println. They are now reported with @warn, including the line number and file name. With strict=true they throw instead.
• The delimiter is now simply the first = or : on the line.
• get_bool read any typo, such as Ture, as false. It now accepts 1/yes/true/on and 0/no/false/off in any case, and throws an ArgumentError naming the section, key and value for anything else.
• get_bool, get_int and get_float threw a MethodError on a missing key. They now take an optional default; without one they throw KeyError((section, key)). Values that cannot be parsed throw an ArgumentError naming the section, key and value.
• write scrambled sections and keys, because they were stored in Dicts. They are now stored in order, so files round-trip. write emits key = value and puts a blank line between sections.
• Keys and values are stored as Strings (OrderedDict{String,String}) instead of Dict{AbstractString,Union{...}}, so lookups are type-stable.
• get(ini, key, default) is removed. It was the same call as get(ini, section, key) whenever the default was a string (Ambiguity in get function #16).
• A UTF-8 byte order mark and CRLF line endings are accepted.

New features

• Multi-line values: lines indented more than their key continue its value, as in configparser (adapted from Support for mutiline values and optional support for mid-line comments #10).
• Opt-in inline comments with inline_comment_prefixes=(";", "#"). A prefix starts a comment only after whitespace (adapted from strip leading/trailing white space and following inline comments from value #8 and Support for mutiline values and optional support for mid-line comments #10).
• Opt-in key case folding with lowercase_keys=true, like configparser's default optionxform.
• read(Inifile, path_or_io; kwargs...) creates an Inifile and reads into it.
• Two-argument show is a one-line summary, so an Inifile inside a container does not print the whole file. The REPL, print and string still give the full contents.
• Docstrings for every exported function, and a README with examples, the file format, and an upgrade guide.

Breaking changes

• set stores string(value), so get always returns a String. For example, get returns "1.5" after set(ini, "s", "k", 1.5).
• get(ini, section, key) and get(ini, key) return nothing instead of :notfound for a missing key. === :notfound checks do not error, they stop matching.
• get(ini, key, default) is removed. Use get(defaults(ini), key, default).
• get_bool throws for values other than 1/yes/true/on and 0/no/false/off, and yes, on and 1 now read as true (they used to read as false). The typed getters throw a KeyError for missing keys.
• sections, section and defaults return OrderedDicts with String keys and values.
• show(io, ini) and repr(ini) give a one-line summary instead of the file contents. print, string and write still give the contents.
• A line indented more than the previous entry continues that entry's value.
• Inifile is an immutable struct with a keyword constructor.
• Julia 1.6 or later is required (0.5 supported Julia 1.0).

Infrastructure

• [compat] entries for julia (1.6) and every dependency. OrderedCollections (1.6, 2) is the only new dependency.
• CI runs the latest Julia release on Linux, macOS and Windows, and the oldest supported version (1.6) on Linux, with julia-actions/cache and codecov.
• Dependabot now updates Julia [compat] entries as well as GitHub Actions, monthly, instead of CompatHelper. TagBot is updated to the current template.
• Tests are expanded to 243, including Aqua.jl.

Version

0.6.0. The changes above are breaking, and for 0.x versions Julia's resolver treats a minor bump as breaking, so packages with IniFile = "0.5" keep 0.5 until they opt in.

Closes #16
Closes #20
Supersedes #8 and #10, which have been open since 2014 and 2015; their authors are credited as co-authors of the commit that adds these features.

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