Replace ts-node with the TypeScript language service

[paulbrimicombe]

Addresses #34

Problem

• OOM errors when compiling large numbers of snippets
• This appears to be due to caching etc. in the ts-node package

Solution

• Drop ts-node completely and use the TypeScript Language service directly (this is what ts-node does under the hood)
• Don't write snippets to disk.
• Compile snippets in series instead of parallel
  • I suspect most of the work is CPU rather than I/O so parallelism doesn't actually help much with the compilation time
  • If we really want to parallelise the compilation, we should probably look at workers etc.