Suggestion: Check if libpcre.so library is installed during nimlangserver installation

[aboisvert]

It would be a better experience if there was a dependency check for libpcre.so library during nimlangserver installation otherwise it can lead to errors later on.

This issue relates to #84 as well as as nim-lang/vscode-nim#43.

In the case of vscode, it can lead to mysterious/silent failure which is not obvious to diagnose since one isn't expected to run nimlangserver on its own and therefore the error could not load: libpcre.so(.3|.1|) is never shown directly to the user and the VSCode plugin just mysteriously fails activation.

[nickysn]

I've also opened a PR in the VS code extension, so the error message is shown:
nim-lang/vscode-nim#44
Of course, we can also add dependency checks to the nimble file as well. Or do other things to ensure the dependencies are installed as well.

[arnetheduck]

Why not get rid of the pcre dependency instead? ie with https://github.com/nitely/nim-regex