Set PATH delimiter as per OS to search for Clojure

[susam]

Prior to this change, on Linux or Unix, even if Clojure is available in
one of the paths mentioned in the PATH environment variable, the normal
mode command ,c fails to start Swank server with Clojure. This issue
occurs because semicolon (;) is assumed to be the path delimiter in
the PATH value, so when PATH is, say, /usr/bin:/usr/local/bin and
clojure.jar is available in /usr/local/bin, the search for Clojure
fails because Slimv tries to search for Clojure in a single directory
named /usr/bin:/usr/local/bin. Instead, it should search for Clojure
in two directories named /usr/bin and /usr/local/bin.

This change ensures that on Linux or Unix, colon (:) is interpreted as
the path delimiter in the PATH value. On Windows, semicolon (;) is
used as the path delimiter.

[susam]

I have tested that this change works fine on Debian, macOS, and Windows.

Testing Steps on Debian, Ubuntu, or macOS

1. Install Maven.

   # On Debian, Ubuntu, etc.
   apt-get update
   apt-get install maven
   
   # On macOS
   brew install openjdk maven
   export JAVA_HOME=/usr/local/opt/openjdk
   export PATH="$JAVA_HOME/bin:$PATH"

2. Install Clojure.

   git clone https://github.com/clojure/clojure.git ~/clj
   git -C ~/clj checkout clojure-1.10.1
   mvn -f ~/clj/pom.xml -Plocal -Dmaven.test.skip=true package
   java -jar ~/clj/clojure.jar -e '(clojure-version)'

3. Install Slimv.

   git clone https://github.com/kovisoft/slimv.git ~/.vim/bundle/slimv
   echo 'set runtimepath^=~/.vim/bundle/slimv' >> ~/.vimrc
   vim +'helptags ~/.vim/bundle/slimv/doc' +q

4. Add Clojure directory to PATH environment variable.

   export PATH=~/clj:$PATH

5. Run Vim within tmux, GNU Screen, or a desktop environment to create
   a new Clojure source file.

   vim foo.clj

6. Press ,c to start Swank server with Clojure. Without this change, Swank server fails to start.

7. Apply this change.

   cd ~/.vim/bundle/slimv
   git checkout -b clojure-path
   git pull https://github.com/susam/slimv clojure-path

8. Repeat steps 4 to 6 again. Swank server should start successfully now and the REPL buffer should appear.

Testing Steps on Windows

1. Install 64-bit Vim using 64-bit installer available at https://github.com/vim/vim-win32-installer/releases.

2. Install 64-bit Python 3.7 using Windows x86-64 executable installer available at https://www.python.org/downloads/release/python-375/. Note: It is important that the Python version be 3.7 because the latest Vim available at the previous URL at this time is compiled with support for Python 3.7.

3. Install 64-bit Git from https://git-scm.com/download/win.

4. Install JDK from https://jdk.java.net/13/.

5. Install Maven from https://maven.apache.org/download.cgi.

6. Add the paths to Vim, Python, Git, JDK, and Maven binaries to PATH environment variable.

7. Install Clojure.

   git clone https://github.com/clojure/clojure.git C:\clj
   git -C C:\clj checkout clojure-1.10.1
   mvn -f C:\clj\pom.xml -Plocal -Dmaven.test.skip=true package
   java -jar C:\clj\clojure.jar -e "(clojure-version)"

8. Install Slimv.

   git clone https://github.com/kovisoft/slimv.git %HOMEPATH%\.vim\bundle\slimv
   echo set runtimepath^^=~/.vim/bundle/slimv >> %HOMEPATH%\.vimrc
   vim +"helptags ~\.vim\bundle\slimv\doc" +q

9. Add Clojure directory to PATH environment variable.

   PATH=C:\clj;%PATH%

10. Run Vim within tmux, GNU Screen, or a desktop environment to create a new Clojure source file.

    vim foo.clj

11. Press ,c to start Swank server with Clojure. It should start successfully even without this change. This issue did not affect Windows.

12. Now we need to ensure that we can start Swank server even after applying this change.

    cd %HOMEPATH%\.vim\bundle\slimv
    git checkout -b clojure-path
    git pull https://github.com/susam/slimv clojure-path

13. Kill Swank server running in a separate console window. Then repeat steps 9 to 11 again. Swank server should start successfully again.