Fix pcre2 issue with ripgrep (closes #145) (#148)

* fix(tags): fix rg command if PCRE not available (closes #145)

Some linux distro do not compile ripgrep using the --pcre2 flag.
This commit checks if the --pcre2 flag is available and then tweaks the
ripgrep command accordingly.

At the moment, it will therefore not be possible to filter-out
hexademical color codes from #tags for people that do not have the
--pcre2 flag available. This will be documented in a later commit.

**Important**: the detection of the PCRE availability is done by trying
a simple rg search using _os.execute_. This function interface was
changed in Lua 5.2, which means it will break when Neovim will update to
Lua >5.1. The fix is already there in commented form.

Fixes #145

* refact: cleanup

* doc(tag): add note about rg --pcre2

* doc(tag): add note about rg --pcre2 in vim help

lua/telekasten.lua

@@ -2734,6 +2734,7 @@ local function FindAllTags(opts)
     opts.tag_notation = M.Cfg.tag_notation
     local templateDir = Path:new(M.Cfg.templates):make_relative(M.Cfg.home)
     opts.templateDir = templateDir
+    opts.rg_pcre = M.Cfg.rg_pcre
 
     if not global_dir_check() then
         return
@@ -2913,6 +2914,16 @@ local function Setup(cfg)
     M.Cfg.dailies = make_config_path_absolute(M.Cfg.dailies)
     M.Cfg.weeklies = make_config_path_absolute(M.Cfg.weeklies)
     M.Cfg.templates = make_config_path_absolute(M.Cfg.templates)
+
+    -- Check if ripgrep is compiled with --pcre
+    -- ! This will need to be fixed when neovim moves to lua >=5.2 by the following:
+    -- M.Cfg.rg_pcre = os.execute("echo 'hello' | rg --pcr2 hello &> /dev/null") or false
+
+    M.Cfg.rg_pcre = false
+    local has_pcre = os.execute("echo 'hello' | rg --pcre2 hello &> /dev/null")
+    if has_pcre == 0 then
+        M.Cfg.rg_pcre = true
+    end
 end
 
 M.find_notes = FindNotes