mxml: Add version 2.12

[Description][1]:

> Mini-XML is a tiny XML library that you can use to read and write XML
> and XML-like data files in your application without requiring large
> non-standard libraries. Mini-XML only requires an ANSI C compatible
> compiler (GCC works, as do most vendors’ ANSI C compilers) and a make
> program.
>
> Mini-XML supports reading of UTF-8 and UTF-16 and writing of UTF-8
> encoded XML files and strings. Data is stored in a linked-list tree
> structure, preserving the XML data hierarchy, element names,
> attributes, and attribute values are supported with no preset limits,
> just available memory.

Lurch depends on this library.

Create the bee file with the command below.

    $ bee init https://github.com/michaelrsweet/mxml/releases/download/v2.12/mxml-2.12.tar.gz
    creating mxml-2.12-0.bee from template '/etc/default/bee/templates/fallback'

[1]: https://www.msweet.org/mxml/

mxml-2.12-0.bee

@@ -0,0 +1,77 @@
+#!/usr/bin/env beesh
+
+## this file was created by bee init and should be executed to build a
+## bee-package. (Additional hints are located at the end of this file.)
+
+###############################################################################
+## The source URL(s) define the location of the sources that will be
+## downloaded. Version variables may be used to simplify reuse of this bee-file.
+
+SRCURL[0]="https://github.com/michaelrsweet/mxml/releases/download/v${PKGVERSION}/mxml-${PKGVERSION}.tar.gz"
+
+###############################################################################
+## Add URLs/pathes to patch files to the PATCHURL array.
+## The sources will be patched in the order of the array.
+
+# PATCHURL+=()
+
+###############################################################################
+## Uncomment the next statement, if the software may not be able to be built
+## outside the source directory and needs to be built inside the source
+## directory.
+
+# build_in_sourcedir
+
+###############################################################################
+## bee cannot detect buildtypes specified in subdirectories.
+## Sometimes packages "hide" the real sources in a subdirectory named
+## 'src' or 'cmake' or ..
+## use 'sourcesubdir_append' to specify this directory if known.
+
+# sourcesubdir_append src
+
+
+###############################################################################
+## Change the default (auto-detected) steps to
+## extract, patch, configure/setup, build and install the software.
+## Make sure the mee_install function does install everything to the
+## image directory "${D}"
+
+#mee_extract() {
+#    bee_extract "${@}"
+#}
+
+#mee_patch() {
+#    bee_patch "${@}"
+#}
+
+#mee_configure() {
+#    bee_configure
+#}
+
+#mee_build() {
+#    bee_build
+#}
+
+#mee_install() {
+#    bee_install
+#}
+## by default this may be 'make install DESTDIR="${D}"'
+
+###############################################################################
+##
+## Additional hints:
+##
+## The name of this bee-file should follow the following naming convention:
+##     pkgname-pkgversion-pkgrevision.bee
+##
+## You may remove all comments as long as SRCURL[0] is set.
+##
+## Everything in this file will be executed in a bash environment.
+##
+## Build the package by executing
+##     './pkg-version-N.bee' or
+##     'beesh ./pkg-version-N.bee'
+##
+## see http://beezinga.org/
+##