Revert textLength approach for character alignment

textLength with lengthAdjust distorts glyphs badly. Use standard
x positioning instead - slight gaps with box-drawing chars are
preferable to distorted text.

Test coverage at 80%.

Bump version to 0.3.4

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "textual-webterm"
-version = "0.3.3"
+version = "0.3.4"
 description = "Serve terminal sessions over the web"
 authors = ["Will McGugan <will@textualize.io>"]
 license = "MIT"