Support guzzlehttp/psr7 v2

Adds support for guzzlehttp/psr7 v2, thanks to @Nielsvanpach

Fix for php8

Fixes "SplFixedArray usage is incompatible with PHP 8.0" #151 thanks to @phpfui in #154

Header consts

• Add header constants (thanks @ThomasLandauer), see updated readme for examples and https://mail-mime-parser.org/api/1.3/classes/ZBateson.MailMimeParser.Header.HeaderConsts.html for full API
• Updated mb-wrapper to 1.0.1 to address an issue with CP1258 (new version of mb-wrapper fixes #141)
• Fix subject headers with consecutive spaces #127
• Don't handle tokens in AddressBaseConsumer #148
• Add E_USER_DEPRECATED notices to deprecated calls

Fix handling for Return-Path

Return-Path should be handled as an AddressHeader ( #138 thanks @mariuszkrzaczkowski )

Fix for multipart/ content types

Defaults to multipart/mixed for any multipart type that isn't known #115

Deprecation of getContentResourceHandle, fix for IdHeader

• Deprecate getContentResourceHandle #106
• Use latest zbateson/stream-decorators
• Mime-encoded headers for IdHeader #109
• Travis testing for php 7.4

Enhancement to allow changing encoding of attachment, and various bug fixes

Enhancement:

• Adds ability to pass encoding (modified addAttachmentPart, addAttachmentPartFromFile with additional optional parameter), #98

Bug fixes:

• "UT" timezone is not correctly handled by PHP #97 (thanks @pupaxxo )
• Don't treat an incorrect header the same as a correct one (contenttype is not the same as content-type if both are set as headers) #102
• Use normalized header name when generating header object based on header name #102

Fix for parsing content with charset=binary

1.1.7 fix didn't work for #95

Delivered-To header support and bugfix for charset=binary

• Add Delivered-To to the list of Address headers #94 (thanks @SunMar )
• Mail with image couldn't be parsed successfully #95

Fix for PHP 7.3 regex compilation error

Fixes preg_split(): Compilation failed: escape sequence is invalid #92