Add .tcl.in file extension

[xdelaruelle]

Add the .tcl.in file extension to the Tcl programming language.

Add init.tcl.in sample file, from the Modules project [1], which is
licensed GPLv2+.

This commit also re-order the available extensions for Tcl as .adp was
not correctly sorted.

[1] https://github.com/cea-hpc/modules

Description

This pull request adds the .tcl.in extension as a Tcl file. .in files are input files: files containing macros that should be translated to obtain an operational file.

Checklist:

• I am associating a language with a new file extension.
  • The new extension is used in hundreds of repositories on GitHub.com
    • Search results for each extension:
      • https://github.com/search?utf8=%E2%9C%93&type=Code&ref=searchresults&q=extension%3Atcl.in+proc+NOT+nothack
      • Not sure the search engine correctly handles extension names with a dot character in it. At least when looking at code source a lot of reference to *.tcl.in files are found: https://github.com/search?q=tcl.in+NOT+nothack&type=code
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • https://github.com/cea-hpc/modules/blob/master/tcl/init.tcl.in
    • Sample license(s): GPLv2+
  • I have included a change to the heuristics to distinguish my language from others using the same extension.